Membrane-mediated amyloidogenesis and the promotion of oxidative lipid damage by amyloid beta proteins

Α-synuclein misfolding and Parkinson's disease

Substantial evidence links α-synuclein, a small highly conserved presynaptic protein with unknown function, to both familial and sporadic Parkinson's disease (PD). α-Synuclein has been identified as the major component of Lewy bodies and Lewy neurites, the characteristic proteinaceous deposits that are the hallmarks of PD. α-Synuclein is a typical intrinsically disordered protein, but can adopt a number of different conformational states depending on conditions and cofactors. These include the helical membrane-bound form, a partially-folded state that is a key intermediate in aggregation and fibrillation, various oligomeric species, and fibrillar and amorphous aggregates. The molecular basis of PD appears to be tightly coupled to the aggregation of α-synuclein and the factors that affect its conformation. This review examines the different aggregation states of α-synuclein, the molecular mechanism of its aggregation, and the influence of environmental and genetic factors on this process.

Role of amyloid-β–metal interactions in Alzheimer’s disease

There is an evolving field of metallobiology that has begun to describe a key role for bioavailable metals (particularly copper, zinc and iron) in the pathogenesis of Alzheimer’s disease (AD). In particular, there is an apparent failure in metal ion homeostasis, potentially caused by a pathological mislocalization of the metals in the brain, which appears to be an obligatory step in both the precipitation and potentiation of the disease. A number of both preclinical and clinical studies have also provided a strong burden of proof that normalizing metal ion homeostasis represents a valid therapeutic target, and may indeed represent the first disease-modifying strategy for AD. The role of metals in the pathophysiology of AD will be discussed in this article.

Oxidative stress and cell membranes in the pathogenesis of Alzheimer's disease

Amyloid β proteins and oxidative stress are believed to have central roles in the development of Alzheimer's disease. Lipid membranes are among the most vulnerable cellular components to oxidative stress, and membranes in susceptible regions of the brain are compositionally distinct from those in other tissues. This review considers the evidence that membranes are either a source of neurotoxic lipid oxidation products or the target of pathogenic processes involving amyloid β proteins that cause permeability changes or ion channel formation. Progress toward a comprehensive theory of Alzheimer's disease pathogenesis is discussed in which lipid membranes assume both roles and promote the conversion of monomeric amyloid β proteins into fibrils, the pathognomonic histopathological lesion of the disease.

Vascular and metabolic dysfunction in Alzheimer's disease: a review

Alzheimer's disease (AD) is thought to start years or decades prior to clinical diagnosis. Overt pathology such as protein misfolding and plaque formation occur at later stages, and factors other than amyloid misfolding contribute to the initiation of the disease. Vascular and metabolic dysfunctions are excellent candidates, as they are well-known features of AD that precede pathology or clinical dementia. While the general notion that vascular and metabolic dysfunctions contribute to the etiology of AD is becoming accepted, recent research suggests novel mechanisms by which these/such processes could possibly contribute to AD pathogenesis. Vascular dysfunction includes reduced cerebrovascular flow and cerebral amyloid angiopathy. Indeed, there appears to be an interaction between amyloid β (Aβ) and vascular pathology, where Aβ production and vascular pathology both contribute to and are affected by oxidative stress. One major player in the vascular pathology is NAD(P)H oxidase, which generates vasoactive superoxide. Metabolic dysfunction has only recently regained popularity in relation to its potential role in AD. The role of metabolic dysfunction in AD is supported by the increased epidemiological risk of AD associated with several metabolic diseases such as diabetes, dyslipidemia and hypertension, in which there is elevated oxidative damage and insulin resistance. Metabolic dysfunction is further implicated in AD as pharmacological inhibition of metabolism exacerbates pathology, and several metabolic enzymes of the glycolytic, tricarboxylic acid cycle (TCA) and oxidative phosphorylation pathways are damaged in AD. Recent studies have highlighted the role of insulin resistance, in contributing to AD. Thus, vascular and metabolic dysfunctions are key components in the AD pathology throughout the course of disease. The common denominator between vascular and metabolic dysfunction emerging from this review appears to be oxidative stress and Aβ. This review also provides a framework for evaluation of current and future therapeutics for AD.

Hydralazine modifies Aβ fibril formation and prevents modification by lipids in vitro

Lipid oxidative damage and amyloid β (Aβ) misfolding contribute to Alzheimer's disease (AD) pathology. Thus, the prevention of oxidative damage and Aβ misfolding are attractive targets for drug discovery. At present, no AD drugs approved by the Food and Drug Administration (FDA) prevent or halt disease progression. Hydralazine, a smooth muscle relaxant, is a potential drug candidate for AD drug therapy as it reduces Aβ production and prevents oxidative damage via its antioxidant hydrazide group. We evaluated the efficacy of hydralazine, and related hydrazides, in reducing (1) Aβ misfolding and (2) Aβ protein modification by the reactive lipid 4-hydroxy-2-nonenal (HNE) using transmission electron microscopy and Western blotting. While hydralazine did not prevent Aβ aggregation as measured using the protease protection assay, there were more oligomeric species observed by electron microscopy. Hydralazine prevented lipid modification of Aβ, and Aβ was used as a proxy for classes of proteins which either misfold or are modified by HNE. All of the other hydrazides prevented lipid modification of Aβ and also did not prevent Aβ aggregation. Surprisingly, a few of the compounds, carbazochrome and niclosamide, appeared to augment Aβ formation. Thus, hydrazides reduced lipid oxidative damage, and hydralazine additionally reduced Aβ misfolding. While hydralazine would require specific chemical modifications for use as an AD therapeutic itself (to improve blood brain barrier permeability, reduce vasoactive side effects, and optimization for amyloid inhibition), this study suggests its potential merit for further AD drug development.

AGEs/RAGE complex upregulates BACE1 via NF-κB pathway activation

Although the pathogenesis of sporadic Alzheimer disease (AD) is not clearly understood, it is likely dependent on several age-related factors. Diabetes is a risk factor for AD, and multiple mechanisms connecting the 2 diseases have been proposed. Hyperglycemia enhances the formation of advanced glycation end products (AGEs) that result from the auto-oxidation of glucose and fructose. The interaction of AGEs with their receptor, named RAGE, elicits the formation of reactive oxygen species that are also believed to be an early event in AD pathology. To investigate a functional link between the disorders diabetes and AD, the effect of 2 AGEs, pentosidine and glyceraldehydes-derived pyridinium (GLAP), was studied on BACE1 expression both in vivo, in streptozotocin treated rats, and in vitro in differentiated neuroblastoma cells. We showed that pentosidine and GLAP were able to upregulate BACE1 expression through their binding with RAGE and the consequent activation of NF-κB. In addition, both pentosidine and GLAP were found to be increased in the brain in sporadic AD patients. Our findings demonstrate that activation of the AGEs/RAGE axis, by upregulating the key enzyme for amyloid-β production, provides a pathologic link between diabetes mellitus and AD.

Oxidative stress mediates the pathogenic effect of different Alzheimer's disease risk factors

Alzheimer's disease (AD) is a progressive neurodegenerative disorder affecting the elderly population. Mechanistically, the major cause of the disease bases on the altered processing of the amyloid-β (Aβ) precursor protein (APP), resulting in the accumulation and aggregation of neurotoxic forms of Aβ. Aβ derives from the sequential proteolytic cleavage of the β- and γ-secretases on APP. The causes of Aβ accumulation in the common sporadic form of AD are not completely known, but they are likely to include oxidative stress (OS). OS and Aβ are linked to each other since Aβ aggregation induces OS in vivo and in vitro, and oxidant agents increase the production of Aβ. Moreover, OS produces several effects that may contribute to synaptic function and cell death in AD. We and others have shown that the expression and activity of β-secretase (named BACE1; β-site APP cleaving enzyme) is increased by oxidant agents and by lipid peroxidation product 4-hydroxynonenal and that there is a significant correlation between BACE1 activity and oxidative markers in sporadic AD. OS results from several cellular insults such as aging, hyperglycemia, hypoxic insults that are all well known risk factors for AD development. Thus, our data strengthen the hypothesis that OS is a basic common pathway of Aβ accumulation, common to different AD risk factors.

The covalent modification of spectrin in red cell membranes by the lipid peroxidation product 4-hydroxy-2-nonenal

Spectrin strengthens the red cell membrane through its direct association with membrane lipids and through protein-protein interactions. Spectrin loss reduces the membrane stability and results in various types of hereditary spherocytosis. However, less is known about acquired spectrin damage. Here, we showed that alpha- and beta-spectrin in human red cells are the primary targets of the lipid peroxidation product 4-hydroxy-2-nonenal (HNE) by immunoblotting and mass spectrometry analyses. The level of HNE adducts in spectrin (particularly alpha-spectrin) and several other membrane proteins was increased following the HNE treatment of red cell membrane ghosts prepared in the absence of MgATP. In contrast, ghost preparation in the presence of MgATP reduced HNE adduct formation, with preferential beta-spectrin modification and increased cross-linking of the HNE-modified spectrins. Exposure of intact red cells to HNE resulted in selective HNE-spectrin adduct formation with a similar preponderance of HNE-beta-spectrin modifications. These findings indicate that HNE adduction occurs preferentially in spectrin at the interface between the skeletal proteins and lipid bilayer in red cells and suggest that HNE-spectrin adduct aggregation results in the extrusion of damaged spectrin and membrane lipids under physiological and disease conditions.

Phospholipid-induced fibrillation of a prion amyloidogenic determinant at the air/water interface

The peptide fragment 106-126 of prion protein [PrP(106-126)] is a prominent amyloidogenic determinant. We present analysis of PrP(106-126) fibrillation at the air/water interface and, in particular, the relationship between the fibrillation process and interactions of the peptide with phospholipid monolayers. We find that lipid monolayers deposited at the air/water interface induce rapid formation of remarkably highly ordered fibrils by PrP(106-126), and that the extent of fibrillation and fiber organization were dependent upon the presence of negatively charged and unsaturated phospholipids in the monolayers. We also observe that fibrillation was enhanced when PrP(106-126) was injected underneath preassembled phospholipid monolayers, compared to deposition and subsequent compression of mixed monolayers of the peptide and phospholipids. In a broader context, this study demonstrates that Langmuir systems constitute a useful platform for studying lipid interactions of amyloidogenic peptides and lipid-induced fibrillation phenomena.

Site-specific modification of Alzheimer's peptides by cholesterol oxidation products enhances aggregation energetics and neurotoxicity

Accumulation of amyloid beta-peptide (Abeta) and tau aggregates, possibly linked to age-associated deficiencies in protein homeostasis, appear to cause Alzheimer's disease. Schiff-base formation between Abeta and the aldehyde-bearing cholesterol oxidation product 3-beta-hydroxy-5-oxo-5,6-secocholestan-6-al is known to increase Abeta amyloidogenicity. Here, we synthesized Abeta variants site-specifically modified with the cholesterol aldehyde at Asp-1, Lys-16, or Lys-28, rather than studying mixtures. These distinct modifications have a similar effect on the thermodynamic propensity for aggregation, enabling aggregation at low concentrations. In contrast, the modification site differentially influences the aggregation kinetics; Lys-16-modified Abeta formed amorphous aggregates fastest and at the lowest concentration (within 2 h at a concentration of 20 nM), followed by the Lys-28 and Asp-1 conjugates. Also, the aggregates resulting from Abeta Lys-16 cholesterol aldehyde conjugation were more toxic to primary rat cortical neurons than treatment with unmodified Abeta under identical conditions and at the same concentration. Our results show that Abeta modification by cholesterol derivatives, especially at Lys-16, renders it kinetically and thermodynamically competent to form neurotoxic aggregates at concentrations approaching the physiologic concentration of Abeta.

Quantitative analysis of phospholipids containing arachidonate and docosahexaenoate chains in microdissected regions of mouse brain

Phospholipids containing polyunsaturated fatty acyl chains are prevalent among brain lipids, and regional differences in acyl chain distribution appear to have both functional and pathological significance. A method is described in which the combined application of GC and multiple reaction monitoring (MRM) MS yielded precise relative quantitation and approximate absolute quantitation of lipid species containing a particular fatty acyl chain in milligram-sized tissue samples. The method uses targeted MRM to identify specific molecular species of glycerophosphocholine lipids, glycerophospho-ethanolamine lipids, glycerophosphoinositol lipids, glycerophosphoserine lipids, glycero-phosphoglycerol lipids, and phosphatidic acids that contain esterified arachidonate (AA) and docosahexaenoate (DHA) separated during normal phase LC/MS/MS analysis. Quantitative analysis of the AA and DHA in the LC fractions is carried out using negative ion chemical ionization GC/MS and stable isotope dilution strategies. The method has been applied to assess the glycerophospholipid molecular species containing AA and DHA in microdissected samples of murine cerebral cortex and hippocampus. Results demonstrate the potential of this approach to identify regional differences in phospholipid concentration and reveal differences in specific phospholipid species between cortex and hippocampus. These differences may be related to the differential susceptibility of different brain regions to neurodegenerative disorders.

Paradoxical condensation of copper with elevated beta-amyloid in lipid rafts under cellular copper deficiency conditions: implications for Alzheimer disease

Redox-active copper is implicated in the pathogenesis of Alzheimer disease (AD), beta-amyloid peptide (Abeta) aggregation, and amyloid formation. Abeta.copper complexes have been identified in AD and catalytically oxidize cholesterol and lipid to generate H2O2 and lipid peroxides. The site and mechanism of this abnormality is not known. Growing evidence suggests that amyloidogenic processing of the beta-amyloid precursor protein (APP) occurs in lipid rafts, membrane microdomains enriched in cholesterol. beta- and gamma-secretases, and Abeta have been identified in lipid rafts in cultured cells, human and rodent brains, but the role of copper in lipid raft amyloidogenic processing is presently unknown. In this study, we found that copper modulates flotillin-2 association with cholesterol-rich lipid raft domains, and consequently Abeta synthesis is attenuated via copper-mediated inhibition of APP endocytosis. We also found that total cellular copper is associated inversely with lipid raft copper levels, so that under intracellular copper deficiency conditions, Abeta.copper complexes are more likely to form. This explains the paradoxical hypermetallation of Abeta with copper under tissue copper deficiency conditions in AD.

Redox proteomics identification of 4-hydroxynonenal-modified brain proteins in Alzheimer's disease: Role of lipid peroxidation in Alzheimer's disease pathogenesis

Numerous studies have shown that neuronal lipids are highly susceptible to oxidative stress including in those brain areas directly involved in the neurodegenerative process of Alzheimer's disease (AD). Lipid peroxidation directly damages membranes and also generates a number of secondary biologically active products (toxic aldehydes)that are capable of easily attacking lipids, proteins, and DNA. Accumulating evidence has demonstrated regionally increased brain lipid peroxidation in patients with AD; however, extensive studies on specific targets of lipid peroxidation-induced damage are still missing. The present study represents a further step in understanding the relationship between oxidative modification of protein and neuronal death associated with AD. We used a proteomics approach to determine specific targets of lipid peroxidation in AD brain, both in hippocampus and inferior parietal lobule, by coupling immunochemical detection of 4-hydroxynonenal-bound proteins with 2-D polyacrylamide gel electrophoresis and MS analysis. We identified 4-hydroxynonenal-bound proteins in the hippocampus and inferior parietal lobule brain regions of subjects with AD. The identified proteins play different biological functions including energy metabolism, antioxidant system, and structural proteins, thus impairing multiple molecular pathways. Our results provide further evidence for the role of lipid peroxidation in the pathogenesis of AD.

Mutant presenilin 1 increases the expression and activity of BACE1

Mutations of the presenilin 1 (PS1) gene are the most common cause of early onset familial Alzheimer disease (FAD). PS1 mutations alter the activity of the gamma-secretase on the beta-amyloid precursor protein (APP), leading to selective overproduction of beta-amyloid (Abeta) 42 peptides, the species that forms oligomers that may exert toxic effects on neurons. Here we show that PS1 mutations, expressed both transiently and stably, in non-neuronal and neuronal cell lines increase the expression and the activity of the beta-secretase (BACE1), the rate-limiting step of Abeta production. Also, BACE1 expression and activity are elevated in brains of PS1 mutant knock-in mice compared with wild type littermates as well as in cerebral cortex of FAD cases bearing various PS1 mutations compared with in sporadic AD cases and controls. The up-regulation of BACE1 by PS1 mutations requires the gamma-secretase cleavage of APP and is proportional to the amount of secreted Abeta42. Abeta42, and not AICD (APP intracellular domain), is indeed the APP derivative that mediates the overexpression of BACE1. The effect of PS1 mutations on BACE1 may contribute to determine the wide clinical and pathological phenotype of early onset FAD.

Reduction of oxidative stress, amyloid deposition, and memory deficit by manganese superoxide dismutase overexpression in a transgenic mouse model of Alzheimer's disease

In Alzheimer's disease (AD), oxidative stress is present early and contributes to disease pathogenesis. We previously reported that in Tg19959 transgenic AD mice, partial deficiency of the mitochondrial antioxidant enzyme manganese superoxide dismutase (MnSOD) exacerbated amyloid pathology. We therefore asked whether MnSOD overexpression would prove beneficial against AD pathogenesis, by studying the offspring of Tg19959 mice crossed with MnSOD-overexpressing mice. At 4 mo of age, there was a 2- to 3-fold increase in MnSOD protein levels in Tg19959-MnSOD mice compared to Tg19959 littermates. Tg19959-MnSOD mice also had a 50% increase in catalase protein levels, a 50% decrease in levels of oxidized protein, and a 33% reduction in cortical plaque burden compared to Tg19959 littermates. Spatial memory was impaired and synaptophysin levels were decreased in Tg19959 mice compared to wild-type littermates, but memory and synaptophysin levels were restored to wild-type levels in Tg19959-MnSOD littermates. These benefits occurred without changes in sodium dodecyl sulfate-soluble or formic acid-soluble Abeta pools or Abeta oligomers in Tg19959-MnSOD mice compared to Tg19959 littermates. These data demonstrate that facilitation of the mitochondrial antioxidant response improves resistance to Abeta, slows plaque formation or increases plaque degradation, and markedly attenuates the phenotype in a transgenic AD mouse model.

Antioxidants in central nervous system diseases: preclinical promise and translational challenges

Oxidative damage is strongly implicated in the pathogenesis of neurodegenerative diseases including Alzheimer's disease, amyotrophic lateral sclerosis, Huntington's disease, Parkinson's disease and stroke (brain ischemia/reperfusion injury). The availability of transgenic and toxin-inducible models of these conditions has facilitated the preclinical evaluation of putative antioxidant agents ranging from prototypic natural antioxidants such as vitamin E (alpha-tocopherol) to sophisticated synthetic free radical traps and catalytic oxidants. Literature review shows that antioxidant therapies have enjoyed general success in preclinical studies across disparate animal models, but little benefit in human intervention studies or clinical trials. Recent high-profile failures of vitamin E trials in Parkinson's disease, and nitrone therapies in stroke, have diminished enthusiasm to pursue antioxidant neuroprotectants in the clinic. The translational disappointment of antioxidants likely arises from a combination of factors including failure to understand the drug candidate's mechanism of action in relationship to human disease, and failure to conduct preclinical studies using concentration and time parameters relevant to the clinical setting. This review discusses the rationale for using antioxidants in the prophylaxis or mitigation of human neurodiseases, with a critical discussion regarding ways in which future preclinical studies may be adjusted to offer more predictive value in selecting agents for translation into human trials.

Sequestration of copper from beta-amyloid promotes selective lysis by cyclen-hybrid cleavage agents

Decelerated degradation of beta-amyloid (Abeta) and its interaction with synaptic copper may be pathogenic in Alzheimer disease. Recently, Co(III)-cyclen tagged to an aromatic recognition motif was shown to degrade Abeta in vitro. Here, we report that apocyclen attached to selective Abeta recognition motifs (KLVFF or curcumin) can capture copper bound to Abeta and use the Cu(II) in place of Co(III) to become proteolytically active. The resultant complexes interfere with Abeta aggregation, degrade Abeta into fragments, preventing H2O2 formation and toxicity in neuronal cell culture. Because Abeta binds Cu in amyloid plaques, apocyclen-tagged targeting molecules may be a promising approach to the selective degradation of Abeta in Alzheimer disease. The principle of copper capture could generalize to other amyloidoses where copper is implicated.

Therapeutics for Alzheimer's disease based on the metal hypothesis

Alzheimer's disease is the most common form of dementia in the elderly, and it is characterized by elevated brain iron levels and accumulation of copper and zinc in cerebral beta-amyloid deposits (e.g., senile plaques). Both ionic zinc and copper are able to accelerate the aggregation of Abeta, the principle component of beta-amyloid deposits. Copper (and iron) can also promote the neurotoxic redox activity of Abeta and induce oxidative cross-linking of the peptide into stable oligomers. Recent reports have documented the release of Abeta together with ionic zinc and copper in cortical glutamatergic synapses after excitation. This, in turn, leads to the formation of Abeta oligomers, which, in turn, modulates long-term potentiation by controlling synaptic levels of the NMDA receptor. The excessive accumulation of Abeta oligomers in the synaptic cleft would then be predicted to adversely affect synaptic neurotransmission. Based on these findings, we have proposed the "Metal Hypothesis of Alzheimer's Disease," which stipulates that the neuropathogenic effects of Abeta in Alzheimer's disease are promoted by (and possibly even dependent on) Abeta-metal interactions. Increasingly sophisticated pharmaceutical approaches are now being implemented to attenuate abnormal Abeta-metal interactions without causing systemic disturbance of essential metals. Small molecules targeting Abeta-metal interactions (e.g., PBT2) are currently advancing through clinical trials and show increasing promise as disease-modifying agents for Alzheimer's disease based on the "metal hypothesis."

Age-dependent neurodegeneration accompanying memory loss in transgenic mice defective in mitochondrial aldehyde dehydrogenase 2 activity

Oxidative stress may underlie age-dependent memory loss and cognitive decline. Toxic aldehydes, including 4-hydroxy-2-nonenal (HNE), an end product of lipid peroxides, are known to accumulate in the brain in neurodegenerative disease. We have previously shown that mitochondrial aldehyde dehydrogenase 2 (ALDH2) detoxifies HNE by oxidizing its aldehyde group. To investigate the role of such toxic aldehydes, we produced transgenic mice, which expressed a dominant-negative form of ALDH2 in the brain. The mice had decreased ability to detoxify HNE in their cortical neurons and accelerated accumulation of HNE in the brain. Consequently, their lifespan was shortened and age-dependent neurodegeneration and hyperphosphorylation of tau were observed. Object recognition and Morris water maze tests revealed that the onset of cognitive impairment correlated with the degeneration, which was further accelerated by APOE (apolipoprotein E) knock-out; therefore, the accumulation of toxic aldehydes is by itself critical in the progression of neurodegenerative disease, which could be suppressed by ALDH2.

Why is the amyloid beta peptide of Alzheimer's disease neurotoxic?

In this article, we support the case that the neurotoxic agent in Alzheimer's disease is a soluble aggregated form of the amyloid beta peptide (Abeta), probably complexed with divalent copper. The structure and chemical properties of the monomeric peptide and its Cu(ii) complex are discussed, as well as what little is known about the oligomeric species. Abeta oligomers are neurotoxic by a variety of mechanisms. They adhere to plasma and intracellular membranes and cause lesions by a combination of radical-initiated lipid peroxidation and formation of ion-permeable pores. In endothelial cells this damage leads to loss of integrity of the blood-brain barrier and loss of blood flow to the brain. At synapses, the oligomers close neuronal insulin receptors, mirroring the effects of Type II diabetes. In intracellular membranes, the most damaging effect is loss of calcium homeostasis. The oligomers also bind to a variety of substances, mostly with deleterious effects. Binding to cholesterol is accompanied by its oxidation to products that are themselves neurotoxic. Possibly most damaging is the binding to tau, and to several kinases, that results in the hyperphosphorylation of the tau and abrogation of its microtubule-supporting role in maintaining axon structure, leading to diseased synapses and ultimately the death of neurons. Several strategies are presented and discussed for the development of compounds that prevent the oligomerization of Abeta into the neurotoxic species.

Site-specific Effects of Peptide Lipidation on β-Amyloid Aggregation and Cytotoxicity

Beta-amyloid (Abeta) aggregates at low concentrations in vivo, and this may involve covalently modified forms of these peptides. Modification of Abeta by 4-hydroxynonenal (4-HNE) initially increases the hydrophobicity of these peptides and subsequently leads to additional reactions, such as peptide cross-linking. To model these initial events, without confounding effects of subsequent reactions, we modified Abeta at each of its amino groups using a chemically simpler, close analogue of 4-HNE, the octanoyl group: K16-octanoic acid (OA)-Abeta, K28-OA-Abeta, and Nalpha-OA-Abeta. Octanoylation of these sites on Abeta-(1-40) had strikingly different effects on fibril formation. K16-OA-Abeta and K28-OA-Abeta, but not Nalpha-OA-Abeta, had increased propensity to aggregate. The type of aggregate (electron microscopic appearance) differed with the site of modification. The ability of octanoyl-Abeta peptides to cross-seed solutions of Abeta was the inverse of their ability to form fibrils on their own (i.e. Abeta approximately Nalpha-OA-Abeta>>K16-OA-Abeta>>K28-OA-Abeta). By CD spectroscopy, K16-OA-Abeta and K28-OA-Abeta had increased beta-sheet propensity compared with Abeta-(1-40) or Nalpha-OA-Abeta. K16-OA-Abeta and K28-OA-Abeta were more amphiphilic than Abeta-(1-40) or Nalpha-OA-Abeta, as shown by lower "critical micelle concentrations" and higher monolayer collapse pressures. Finally, K16-OA-Abeta and K28-OA-Abeta are much more cytotoxic to N2A cells than Abeta-(1-40) or Nalpha-OA-Abeta. The greater cytotoxicity of K16-OA-Abeta and K28-OA-Abeta may reflect their greater amphiphilicity. We conclude that lipidation can make Abeta more prone to aggregation and more cytotoxic, but these effects are highly site-specific.