Solvent effects on beta protein toxicity in vivo

Aminocyclodextrin Oligomers as Protective Agents of Protein Aggregation

Over 30 different amyloid proteins and a number of corresponding protein-misfolding diseases have been identified. Among these is Alzheimer's disease, the most common neurodegenerative disorder. The treatment of these diseases is still a goal to reach and many molecules have been studied in this context. Among these, the cyclodextrins have shown interesting potential as agents against protein aggregation (antiaggregants). On the basis of this interest, we investigated the effect on protein aggregation of some oligomers of β-cyclodextrins. In particular, it was found that amino oligomers show good inhibition of β-amyloid aggregation in the micromolar concentration range. The presence of both a multicavity system and amino groups seems to be essential for preventing protein aggregation.

Cyclodextrins as Protective Agents of Protein Aggregation: An Overview

Cyclodextrins are extensively used in different fields (e.g., catalysis, chromatography, pharma, supramolecular chemistry, bioorganic chemistry, and bioinorganic chemistry), and their applications have been widely reviewed. Their main application in the field of pharmaceutical is as a drug carrier. This review overviews, for the first time, the use of cyclodextrins and their derivatives as antiaggregant agents in a number of proteins (e.g., amyloid-β, insulin, recombinant human growth hormone, prion protein, transthyretin, and α-synuclein) and some multimeric enzymes. There are many diseases that are correlated to protein misfolding and amyloid formation processes affecting numerous organs and tissues. There are over 30 different amyloid proteins and a number of corresponding diseases. Alzheimer's disease is the most common neurodegenerative disease. Treatment of these diseases is still a goal to reach, and many molecules are studied in this perspective. Cyclodextrins have also been studied, and they show great potential; as such, further studies could be very promising. This review aims to be a stimulus for the design of new cyclodextrin derivatives to obtain multifunctional systems with antiaggregant activity.

Unusual Cyclodextrin Derivatives as a New Avenue to Modulate Self- and Metal-Induced Aβ Aggregation

Mounting evidence suggests an important role of cyclodextrins in providing protection in neurodegenerative disorders. Metal dyshomeostasis is reported to be a pathogenic factor in neurodegeneration because it could be responsible for damage involving oxidative stress and protein aggregation. As such, metal ions represent an effective target. To improve the metal-binding ability of cyclodextrin, we synthesized three new 8-hydroxyquinoline-cyclodextrin conjugates with difunctionalized cyclodextrins. In particular, the 3-difunctionalized regioisomer represents the first example of cyclodextrin with two pendants at the secondary rim, resulting in a promising compound. The derivatives have significant antioxidant capacity and the powerful activity in inhibiting self-induced amyloid-β aggregation seems to be led by synergistic effects of both cyclodextrin and hydroxyquinoline. Moreover, the derivatives are also able to complex metal ions and to inhibit metal-induced protein aggregation. Therefore, these compounds could have potential as therapeutic agents in diseases related to protein aggregation and metal dyshomeostasis.

Letter: β-Cyclodextrin affects the formation of isomerization products during peptide deamidation

Cyclodextrins (CDs) are a group of nontoxic oligosaccharides that are widely used as drug excipients and protein stabilizers. CDs have also been found to reduce the neurotoxicity and fibrillation of amyloid beta (Aβ), the major component of the amyloid plaques found in the brain of patients suffering from Alzheimer's disease. The formation of these plaques was found to be enhanced by the presence of iso-aspartic acid (isoAsp) residues in the Aβ peptide, which can be formed by deamidation from asparagine (Asn). To explore further the influence of CDs on Aβ, we investigated three Asn-containing peptides, including Aβ25-35, by electrospray ionization, electron capture dissociation, and Fourier-transform ion cyclotron resonance mass spectrometry to explore details of the deamidation process in the presence and absence of peptide/CD adducts. The results showed that CDs reduced the formation of the isomerization product isoAsp during peptide deamidation. This finding might help to better understand the role of CDs during the protein-aggregation process.

Multifunctional 8-hydroxyquinoline-appended cyclodextrins as new inhibitors of metal-induced protein aggregation

Mounting evidence suggests a pivotal role of metal imbalances in protein misfolding and amyloid diseases. As such, metal ions represent a promising therapeutic target. In this context, the synthesis of chelators that also contain complementary functionalities to combat the multifactorial nature of neurodegenerative diseases is a highly topical issue. We report two new 8-hydroxyquinoline-appended cyclodextrins and highlight their multifunctional properties, including their Cu(II) and Zn(II) binding abilities, and capacity to act as antioxidants and metal-induced antiaggregants. In particular, the latter property has been applied in the development of an effective assay that exploits the formation of amyloid fibrils when β-lactoglobulin A is heated in the presence of metal ions.

Dye-binding assays for evaluation of the effects of small molecule inhibitors on amyloid (aβ) self-assembly

Dye-binding assays, such as those utilizing Congo red and thioflavin T, are among the most widely used tools to probe the aggregation of amyloidogenic biomolecules and for the evaluation of small molecule inhibitors of amyloid aggregation and fibrillization. A number of recent reports have indicated that these dye-binding assays could be prone to false positive effects when assessing inhibitors' potential toward Aβ peptides, species involved in Alzheimer's disease. Specifically, this review focuses on the application of thioflavin T for determining the efficiency of small molecule inhibitors of Aβ aggregation and addresses potential reasons that might be associated with the false positive effects in an effort to increase reliability of dye-binding assays.

Specific binding of a β-cyclodextrin dimer to the amyloid β peptide modulates the peptide aggregation process

Alzheimer's disease involves progressive neuronal loss. Linked to the disease is the amyloid β (Aβ) peptide, a 38-43-amino acid peptide found in extracellular amyloid plaques in the brain. Cyclodextrins are nontoxic, cone-shaped oligosaccharides with a hydrophilic exterior and a hydrophobic cavity making them suitable hosts for aromatic guest molecules in water. β-Cyclodextrin consists of seven α-d-glucopyranoside units and has been shown to reduce the level of fibrillation and neurotoxicity of Aβ. We have studied the interaction between Aβ and a β-cyclodextrin dimer, consisting of two β-cyclodextrin monomers connected by a flexible linker. The β-cyclodextrin monomer has been found to interact with Aβ(1-40) at sites Y10, F19, and/or F20 with a dissociation constant (K(D)) of 3.9 ± 2.0 mM. Here (1)H-(15)N and (1)H-(13)C heteronuclear single-quantum correlation nuclear magnetic resonance (NMR) spectra show that in addition, the β-cyclodextrin monomer and dimer bind to the histidines. NMR translational diffusion experiments reveal the increased affinity of the β-cyclodextrin dimer (apparent K(D) of 1.1 ± 0.5 mM) for Aβ(1-40) compared to that of the β-cyclodextrin monomer. Kinetic aggregation experiments based on thioflavin T fluorescence indicate that the dimer at 0.05-5 mM decreases the lag time of Aβ aggregation, while a concentration of 10 mM increases the lag time. The β-cyclodextrin monomer at a high concentration decreases the lag time of the aggregation. We conclude that cyclodextrin monomers and dimers have specific, modulating effects on the Aβ(1-40) aggregation process. Transmission electron microscopy shows that the regular fibrillar aggregates formed by Aβ(1-40) alone are replaced by a major fraction of amorphous aggregates in the presence of the β-cyclodextrin dimer.

Direct solid-phase synthesis of the beta-amyloid (1-42) peptide using controlled microwave heating

Standard linear Fmoc/t-Bu solid-phase synthesis of the 42-mer beta-amyloid (1-42) peptide was achieved under controlled microwave conditions at 86 degrees C using inexpensive DIC/HOBt as coupling reagent on ChemMatrix resin. In order to avoid racemization of the sensitive amino acids, the coupling of the three His residues in the difficult peptide sequence was performed at room temperature. The desired peptide was obtained within 15 h overall processing time in high yield and purity (78% crude yield).

Controlled in situ preparation of A beta(1-42) oligomers from the isopeptide "iso-A beta(1-42)", physicochemical and biological characterization

Beta-amyloid (A beta) peptides play a crucial role in the pathology of the neurodegeneration in Alzheimer's disease (AD). Biological experiments (both in vitro and animal model studies of AD) require synthetic A beta peptides of standard quality, aggregation grade, neurotoxicity and water solubility. The synthesis of A beta peptides has been difficult, owing to their hydrophobic character, poor solubility and high tendency for aggregation. Recently an isopeptide precursor (iso-A beta(1-42)) was synthesized by Fmoc-chemistry and transformed at neutral pH to A beta(1-42) by O-->N acyl migration in a short period of time. We prepared the same precursor peptide using Boc-chemistry and studied the transformation to A beta(1-42) by acyl migration. The peptide conformation and aggregation processes were studied by several methods (circular dichroism, atomic force and transmission electron microscopy, dynamic light scattering). The biological activity of the synthetic A beta(1-42) was measured by ex vivo (long-term potentiation studies in rat hippocampal slices) and in vivo experiments (spatial learning of rats). It was proven that O-->N acyl migration of the precursor isopeptide results in a water soluble oligomeric mixture of neurotoxic A beta(1-42). These oligomers are formed in situ just before the biological experiments and their aggregation grade could be standardized.

Overcoming synthetic Abeta peptide aging: a new approach to an age-old problem

Investigations of amyloidogenic diseases use synthetic peptides for cell-free and in vitro studies. However, amyloidogenic peptides often show intrinsic variability that markedly affects the reproducibility of experiments. Proof of physicochemical and biological variability with different batches of amyloidogenic peptides have been reported in literature. Here, we show that differences can be observed even within the same batch of Abeta1-42 peptide after storing lyophilised samples at -20 degrees C. This change (referred to as 'peptide aging') was reproduced with Abeta1-40 peptide samples by using a series of lyophilisation cycles, showing that lyophilisation, rather than preserving the physicochemical and biological features of Abeta peptides, introduces wide variability. To counteract synthetic peptide aging, we set up a procedure involving the sequential use of trifluoroacetic acid, formic acid and sodium hydroxide solutions that disaggregate preformed seeds and enriched Abeta peptide solutions into monomers and low-molecular-weight oligomers. This procedure enabled us to obtain reproducible physicochemical and biological features of Abeta peptides, irrespective of their age.

Use of copper and insulin-resistance to accelerate cognitive deficits and synaptic protein loss in a rat Abeta-infusion Alzheimer's disease model

The rat amyloid-beta (Abeta) intracerebroventricular infusion can model aspects of Alzheimer's disease (AD) and has predicted efficacy of therapies such as ibuprofen and curcumin in transgenic mouse models. High density lipoprotein (HDL), a normal plasma carrier of Abeta, is used to attenuate Abeta aggregation within the pump, causing Abeta-dependent toxicity and cognitive deficits within 3 months. Our goal was to identify factors that might accelerate onset of Abeta-dependent deficits to improve efficiency and cost-effectiveness of model. We focused on: 1) optimizing HDL-Abeta preparation for maximal toxicity; 2) evaluating the role of copper, a factor typically in water that can impact oligomer stability; and 3) determining impact of insulin resistance (type II diabetes), a risk factor for AD. In vitro studies were performed to determine doses of copper and methods of Abeta-HDL preparation that maximized toxicity. These preparations when infused resulted in earlier onset of cognitive deficits within 6 weeks post-infusion. Induction of insulin resistance did not exacerbate Abeta-dependent cognitive deficits, but did exacerbate synaptic protein loss. In summary, the newly described in vivo infusion model may be useful cost-effective method for screening for new therapeutic drugs for AD.

Synthesis of Abeta[1-42] and its derivatives with improved efficiency

It has been proved that the principal component of senile plaques is aggregates of beta-amyloid peptide (Abeta) in cases of one of the most common forms of age-related neurodegenerative disorders, Alzheimer's disease (AD). Although the synthetic methods for the synthesis of Abeta peptides have been developed since their first syntheses, Abeta[1-42] is still problematic to prepare. The highly hydrophobic composition of Abeta[1-42] results in aggregation between resin-bound peptide chains or intrachain aggregation which leads to a decrease in the rates of deprotection and repetitive incomplete coupling reactions during 9-flurenylmethoxycarbonyl (Fmoc) synthesis. In order to avoid aggregation and/or disrupt internal aggregation during stepwise Fmoc solid phase synthesis and to improve the quality of crude products, several attempts have been made. Since highly pure Abeta peptides in large quantities are used in biological experiments, we wanted to develop a method for a rational synthesis of human Abeta[1-42] with high purity and adequate yield. This paper reports a convenient methodology with a novel solvent system for the synthesis of Abeta[1-42], its N-terminally truncated derivatives Abeta[4-42] and Abeta[5-42], and Abeta[1-42] labeled with 7-amino-4-methyl-3-coumarinylacetic acid (AMCA) at the N-terminus using Fmoc strategy. The use of 10% anisole in Dimethylformamide/Dichloromethane (DMF/DCM) can substantially improve the purity and yield of crude Abeta[1-42] and has been shown to be an optimal coupling condition for the synthesis of Abeta[1-42]. Anisole is a cheap and simple aid in the synthesis of 'difficult sequences' where other solvents are less successful in the prevention of aggregation during the synthesis.

Effects of a novel cognitive enhancer, spiro[imidazo-[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), on learning impairments induced by amyloid-beta1-40 in the rat

We have previously shown that intracerebroventricular (i.c.v.) infusion of amyloid-beta (Abeta)1-40 produces oxidative stress and cholinergic dysfunction, as well as learning and memory deficits, in rats. In the present study, effects of a newly synthesized azaindolizinone derivative, spiro[imidazo[1,2-a]pyridine-3,2-indan]-2(3H)-one (ZSET1446), were assessed in rats with learning deficits induced by Abeta1-40 or scopolamine. The i.c.v. infusion of Abeta1-40 caused impairments in spontaneous alternation behavior in a Y-maze task, spatial reference and short-term memory in a water-maze task, and retention of passive-avoidance learning. Abeta1-40-infused rats also showed reduction in choline acetyltransferase (ChAT) activity in the medial septum and hippocampus, but not in the basal forebrain and cortex, and a decrease in glutathione S-transferase (GST)-like immunoreactivity in the cortex. Nicotine-stimulated acetylcholine (ACh) release in Abeta1-40-infused rats was lower than that in vehicle-infused rats. Oral administration of ZSET1446 at the dose range of 0.01 to 1 mg/kg ameliorated Abeta1-40-induced learning impairment in Y-maze, water-maze, and passive-avoidance tasks. ZSET1446 reversed the decrease of ChAT activity in the medial septum and hippocampus, GST-like immunoreactivity in the cortex, and nicotine-stimulated ACh release of Abeta1-40-treated rats to the levels of vehicle-infused control rats. Furthermore, 0.001 to 0.1 mg/kg ZSET1446 showed ameliorative effects on learning impairments caused by scopolamine in a passive-avoidance task. These results suggest that ZSET1446 may be a potential candidate for development as a therapeutic agent to manage cognitive impairment associated with conditions such as Alzheimer's disease.

A case for a non-transgenic animal model of Alzheimer's disease

Alzheimer's disease (AD) is associated with an early impairment in memory and is the major cause of dementia in the elderly. beta-Amyloid (Abeta) is believed to be a primary factor in the pathogenic pathway leading to dementia. Mounting evidence suggests that this syndrome begins with subtle alterations in synaptic efficacy prior to extensive neuronal degeneration and that the synaptic dysfunction could be caused by diffusible oligomeric assemblies of Abeta. This paper reviews the findings from behavioral analysis, electrophysiology, neuropathology and nootropic drug screening studies involving exogenous administration of Abeta in normal rodent brains. This non-transgenic model of amyloid pathology in vivo is presented as a complementary alternative model to transgenic mice to study the cellular and molecular pathways induced by amyloid, which in turn may be a causal factor in the disruption of cognition. The data reviewed here confirm that the diffusible form of Abeta rapidly induces synaptic dysfunction and a secondary process involving cellular cascades induced by the fibrillar form of amyloid. The time-course of alteration in memory processes implicates at least two different mechanisms that may be targeted with selective therapies aimed at improving memory in some AD patients.

Active clearance of human amyloid beta 1-42 peptide aggregates from the rat ventricular system

A major constituent of SP in the brains of Alzheimer's disease is 39-43 amino acid peptide called beta-amyloid peptide (Abeta). Recent data have demonstrated that Abeta has a strong tendency to form insoluble aggregates and that toxic effects of Abeta is based on its aggregation. In the current study, 100 microg of human synthetic Abeta 1-42 (sAbeta 1-42) was infused into the lateral ventricle of rat brain using a short-term infusion model. At 2 or 7 days following the infusion, sAbeta 1-42 was found to form insoluble aggregates, scattering throughout the entire ventricular systems. The sAbeta 1-42 aggregates were partially engulfed by phagocytic cells and deposited at the meningeal vessels or the choroid plexuses. However, these deposits mostly disappeared from the ventricles by 28 days post-infusion. Here, it is reported for the first time that considerable amounts of sAbeta 1-42 are almost cleared from the rat ventricular system by the mononuclear phagocytic system.

Acetylcholinesterase-Abeta complexes are more toxic than Abeta fibrils in rat hippocampus: effect on rat beta-amyloid aggregation, laminin expression, reactive astrocytosis, and neuronal cell loss

Neuropathological changes generated by human amyloid-beta peptide (Abeta) fibrils and Abeta-acetylcholinesterase (Abeta-AChE) complexes were compared in rat hippocampus in vivo. Results showed that Abeta-AChE complexes trigger a more dramatic response in situ than Abeta fibrils alone as characterized by the following features observed 8 weeks after treatment: 1). amyloid deposits were larger than those produced in the absence of AChE. In fact, AChE strongly stimulates rat Abeta aggregation in vitro as shown by turbidity measurements, Congo Red binding, as well as electron microscopy, suggesting that Abeta-AChE deposits observed in vivo probably recruited endogenous Abeta peptide; 2). the appearance of laminin expressing neurons surrounding Abeta-AChE deposits (such deposits are resistant to disaggregation by laminin in vitro); 3). an extensive astrocytosis revealed by both glial fibrillary acidic protein immunoreactivity and number counting of reactive hypertrophic astrocytes; and 4). a stronger neuronal cell loss in comparison with Abeta-injected animals. We conclude that the hippocampal injection of Abeta-AChE complexes results in the appearance of some features reminiscent of Alzheimer-like lesions in rat brain. Our studies are consistent with the notion that Abeta-AChE complexes are more toxic than Abeta fibrils and that AChE triggered some of the neurodegenerative changes observed in Alzheimer's disease brains.

Amyloid beta peptide directly inhibits PKC activation

A putative protein kinase C (PKC) pseudosubstrate domain in beta amyloid (Abeta) suggests a potential interaction between Abeta and PKC. In this study, we investigated whether and how Abeta interacts with PKC. Abeta peptides inhibited PKC phosphorylation in a dose-dependent manner in cell-free in vitro condition, suggesting a direct interaction between Abeta and PKC. Experiments involving deletion of the Abeta sequence indicated that the putative PKC pseudosubstrate domain (Abeta 28-30) is critical for Abeta-PKC interaction. Addition of Abeta peptides to cultured B103 cells reduced the activated forms of PKCalpha and PKCepsilon. It also inhibited phorbol-12,13-dibutyrate (PDBu)-induced membrane translocation of PKCalpha and PKCepsilon without altering their expression levels, indicating that activation of intracellular PKC is inhibited by treatment of Abeta peptides. These results suggest that Abeta peptides inhibit PKC activation via direct interactions, which may play a role in pathogenesis of AD.

Per-6-substituted-per-6-deoxy β-cyclodextrins Inhibit the Formation of β-Amyloid Peptide Derived Soluble Oligomers

Recent studies have indicated that the most important role of beta-amyloid peptide (Abeta) in the etiology of Alzheimer's disease may not be in plaque formation but in the formation of soluble, metastable Abeta(1-42) neurotoxic intermediates (called ADDLs). In the present work we describe the preparation of per-6-amino-6-deoxy-beta-cyclodextrins, which inhibit ADDLs formation in vitro.

Human Abeta1-42 reduces iron-induced toxicity in rat cerebral cortex

Senile plaques, the major neuropathological lesions of Alzheimer's disease (AD), are composed primarily of amyloid-beta (Abeta) peptide and contain high concentrations of iron (1.0 mM). We have previously shown that intracortical injections of 1.0 mM iron to adult rats produce significantly more neuronal loss than control injections of saline vehicle, whereas injections of Abeta do not. Because iron has been shown to increase the in vitro toxicity of Abeta, the present study was undertaken to determine whether iron can make Abeta neurotoxic in vivo. Abeta and 1.0 mM iron (as ferric ammonium citrate) were coinjected into rat cerebral cortex, and the neuronal loss was compared with that produced by pure Abeta or pure iron. The human and rat variants of Abeta(1-42) were compared to determine whether they produce the same amount of neuronal loss when combined with iron. Coinjection of iron with either Abeta variant caused significantly more neuronal loss than Abeta peptide alone, suggesting that iron may contribute to the toxicity associated with senile plaques. Rat Abeta(1-42) combined with iron was as toxic as iron alone, whereas iron combined with human Abeta(1-42) was significantly less toxic. This latter finding indicates that fibrillar human Abeta is able to reduce iron-induced neurotoxicity in vivo and raises the interesting possibility that senile plaques in AD may represent a neuroprotective response to the presence of elevated metal ions.

Per-6-substituted beta-cyclodextrin libraries inhibit formation of beta-amyloid-peptide (A beta)-derived, soluble oligomers

Alzheimer's disease is the most common cause of dementia in older individuals with compelling evidence favoring neuron dysfunction and death triggered by assembled forms of A beta(1-42). While large neurotoxic amyloid fibrils have been known for years, recent studies show that soluble protofibril and A beta(1-42)-derived diffusible ligands (ADDLs) may also be involved in neurotoxicity. In the present work, dot-blot immunoassays discriminating ADDLs from monomers were used to screen libraries of per-substituted beta-cyclodextrin (beta-CD) derivatives for inhibition of ADDLs formation. Libraries were prepared from per-6-iodo-beta-CD by treatment with various amine nucleophiles. The most active library tested (containing >2000 derivatives) was derived from imidazole, N, N-dimethylethylenediamine and furfurylamine, which at 10 microM total library, inhibited ADDLs formation (10 nM A beta(1-42)) over a period of 4 hours. The latter was confirmed by a western blot assay showing decreased amounts of the initially formed A beta(1-42) tetramer. These preliminary experiments suggest that derivatized forms of beta-CD can interfere with the oligomerization process of A beta(1-42).

Amyloid precursor protein family-induced neuronal death is mediated by impairment of the neuroprotective calcium/calmodulin protein kinase IV-dependent signaling pathway

The aberrant metabolism of beta-amyloid precursor protein (APP) and the progressive deposition of its derived fragment beta-amyloid peptide are early and constant pathological hallmarks of Alzheimer's disease. Because APP is able to function as a cell surface receptor, we investigated here whether a disruption of the normal function of APP may contribute to the pathogenic mechanisms in Alzheimer's disease. To this aim, we generated a specific chicken polyclonal antibody directed against the extracellular domain of APP, which is common with the beta-amyloid precursor-like protein type 2. Exposure of cultured cortical neurons to this antibody (APP-Ab) induced cell death preceded by neurite degeneration, oxidative stress, and nuclear condensation. Interestingly, caspase-3-like protease was not activated in this neurotoxic action suggesting a different mode of cell death than classical apoptosis. Further analysis of the molecular mechanisms revealed a calpain- and calcineurin-dependent proteolysis of the neuroprotective calcium/calmodulin-dependent protein kinase IV and its nuclear target protein cAMP responsive element binding protein. These effects were abolished by the G protein inhibitor pertussis toxin, strongly suggesting that APP binding operates via a GTPase-dependent pathway to cause neuronal death.

Increased expression of intranuclear AChE involved in apoptosis of SK-N-SH cells

Programmed cell death plays an integral role in neurodegenerative diseases such as Alzheimer's disease (AD). Acetylcholinesterase (AChE) was suggested to be neurotoxic in vivo and in vitro and accelerate assembly of amyloid peptide into Alzheimer's fibrils. In our experiments, we found increased AChE expression in apoptotic neuroblastoma SK-N-SH cells after long-term culture. Our results first showed that in apoptotic SK-N-SH cells, AChE aggregated in the nucleus and suppression of AChE expression with antisense oligonucleotide could save the cells from apoptosis. It was also found that caspase-3 activity was parallel with AChE activation in apoptotic SK-N-SH cells. These results suggest that AChE plays an important role in the procession of neuroblastoma cell apoptosis and favor the association between AChE and neuronal apoptosis in AD.

Structure and location of amyloid beta peptide chains and arrays in Alzheimer's disease: new findings require reevaluation of the amyloid hypothesis and of tests of the hypothesis

New in situ high resolution electronmicroscopic examination of amyloid fibrils in situ indicate that in Alzheimer's disease these fibrils are not simply long chains of self aggregated amyloid beta peptide. The amyloid beta is not only associated with P protein and glycans, as was well known from previous immunohistologic studies, but is arranged in the form of short chains at right angles to a P protein backbone with the glycans wrapped around that backbone. These findings suggest that the hypothesis causally relating simple, fibrillar amyloid beta to Alzheimer's disease must be reevaluated since such simple fibrils may be absent, or not the major form of the amyloid beta in the brain. Other data shows that shorter multimers, so-called protofibrils, or dimers of amyloid beta or molecules cleaved from it can be highly toxic. Some of these may be in the soluble amyloid beta fraction. Shorter multimers or dimers of amyloid beta, either extra or intracellular, may be the real links between amyloid beta production and Alzheimer's disease. Toxicity studies employing fibrillar amyloid beta may not be relevant, even if they produce lesions, because they do not employ amyloid beta in the form in which it actually exists in the Alzheimer brain. Studies of treatments designed to remove fibrils or to prevent their formation may be ineffective or suboptimal in effectiveness because they do not reduce the relevant amyloid burden and/or fail to alter the arrangement of shorter multimers of amyloid beta around its P-protein and glycan core.

Hippocampal injections of amyloid beta-peptide 1-40 impair subsequent one-trial/day reward learning

The injection of amyloid beta-peptide (Abeta) into rat CNS has been reported to induce cellular neuropathology. The present study investigated whether multiple intrahippocampal injections of Abeta 1-40 would impair one-trial/day reward learning 14 days later. Twenty-four male Sprague-Dawley rats, 3-4 months old, were injected with either Abeta 1-40 or distilled water into seven hippocampal sites bilaterally. Ten rats received 3 nmol Abeta 1-40 in 2 microl of distilled water per injection site, while 14 rats received distilled water alone. Following a 9-day recovery period, rats were gradually food deprived to 82% of their initial body weight. Fourteen days after the intrahippocampal injection, all rats received an initial training trial and three subsequent daily retention trials. Rats receiving Abeta 1-40 were significantly impaired on the second retention trial in terms of accuracy (number of unbaited alleys entered) and on the second and third retention trials in terms of speed (reciprocal of latency to reward). Histological analysis showed that Abeta 1-40 injections produced significant neuronal loss and gliosis. Abeta 1-40 immunoreactivity persisted locally at the injection site and in macrophages 2 weeks following the hippocampal injections. These effects appear to be sequence-specific; rats receiving Abeta 1-42 with a scrambled peptide sequence did not differ significantly from rats receiving distilled water alone in retention of the learning task or degree of histological damage.

The effect of age on the response of the rat brains to continuous beta-amyloid infusion

Young (3 months old) and aging (18-21 months old) rats were infused intracerebroventricularly with beta-amyloid (1-40; 4.2 nmol) for 14 days. In both age groups, beta-amyloid led to deficits in water-maze and decreased choline acetyltransferase activity and somatostatin levels. Cortical substance P levels also decreased whereas neuropeptide Y levels remained unaltered. There were no significant age dependent differences among these neurochemicals except a decrease in hippocampal neuropeptide Y levels in the aging group. It is concluded that young and aging rat brains respond similarly to beta-amyloid infusion.

Animal models of Alzheimer's disease and evaluation of anti-dementia drugs

Alzheimer's disease (AD) is the most common cause of progressive decline of cognitive function in aged humans, and is characterized by the presence of numerous senile plaques and neurofibrillary tangles accompanied by neuronal loss. Some, but not all, of the neuropathological alterations and cognitive impairment in AD can be reproduced genetically and pharmacologically in animals. It should be possible to discover novel drugs that slow the progress or alleviate the clinical symptoms of AD by using these animal models. We review the recent progress in the development of animal models of AD and discuss how to use these model animals to evaluate novel anti-dementia drugs.

Protocol for quantitative and qualitative analyses of the in vitro aggregation of synthetic beta-amyloid. A method applicable to the identification of substances that may have therapeutic efficacy for Alzheimer's disease

Biochemical studies of beta-amyloid (Abeta) aggregation have been hampered by the lack of a simple method to examine simultaneously the extent of aggregation and the structural nature of the aggregates. Consequently, often only the extent of aggregation is analyzed and reported. This means that there is often no knowledge of whether the aggregates consist of fibrils, a structure crucial for their neurotoxicity. Here we describe the development of a protocol for quantitatively and qualitatively evaluating the in vitro aggregation of synthetic Abeta. Specifically, a fluorescein derivatized Abeta(1-42) peptide (FITC-Abeta(1-42)) was used as the aggregation material. We found that the fluorescent Abeta peptide aggregated as efficiently as the native ones and the extent of their aggregation could be determined accurately by fluorescence spectrophotometry. Significantly, our approach is also qualitative because it allows a direct structural examination of Abeta fibrils by fluorescence microscopy. In addition, this protocol can also be applied to the identification of substance(s) capable of inhibiting Abeta aggregation and further the assessment of the nature of such inhibition.

APP carboxyl-terminal fragment without or with abeta domain equally induces cytotoxicity in differentiated PC12 cells and cortical neurons

Mutations in the beta-amyloid precursor protein (APP) gene cause familial Alzheimer's disease (AD). Although amyloid beta peptide (Abeta) is the principal constituent of senile plaques in AD, other cleavage products of APP are also implicated in playing a role in the pathogenesis of AD. C-terminal fragments of APP (APP-CTs), that contain complete Abeta sequence, are found in neuritic plaques, neurofibrillary tangles and the cytosol of lymphoblastoid cells obtained from AD patients. Our previous report demonstrated that APP-CT105 causes death of differentiated PC12 cells and cultured rat cortical neurons (Kim and Suh [1996] J. Neurochem. 67:1172-1182) and induces strong inward currents in Xenopus oocyte (Fraser et al., [1996] J. Neurochem. 66:2034-2040). In the present study, to investigate which domain of APP-CT105 is responsible for the neurotoxicity, we have made deletion mutants of APP-CT105 without Abeta and transmembrane domain (TM) or without NPTY domain, a putative endocytosis signaling sequence, using the PCR-amplified strategy and the recombinant GST-fusion protein strategy. The effect on cell survival of the deletion mutants of APP-CT105 (8 microM) was then determined by the LDH and MTT assay. We found that C-terminal fragment without NPTY significantly causes cell death in NGF-differentiated PC12 cells and cultured rat cortical neurons. This finding suggests that NPTY may not play an important role in APP-CT105 mediated neurotoxicity. We found, however, that C-terminal fragment without Abeta and TM significantly induces neuronal cell death. Our results suggest that in addition to Abeta, C-terminal fragment of APP without Abeta and TM domain itself may also participate in the neuronal degeneration in AD.

Repeated intracerebroventricular administration of beta-amyloid(25-35) to rats decreases muscarinic receptors in cerebral cortex

The effects of repeated in vivo administration to rats of beta-amyloid(25-35) (betaA(25-35)) on several cholinergic markers have been studied and compared with those of a peptide with a scrambled sequence. Rats received intracerebroventricular injections of betaA(25-35) (5 or 20 microg/day) for 7 days and they were sacrificed at 2 or 3 weeks survival. The density of total muscarinic receptors labeled with [3H]N-methyl-scopolamine was dose-dependently decreased by betaA(25-35) in the cerebral cortex at 3 weeks survival. No changes were observed at 2 weeks survival in cerebral cortex or in the hippocampus, at any time. BetaA(25-35) administration did not modify choline acetyltranferase activity in cerebral cortex. However, in betaA(25-35)-treated rats hypertrophic/hyperactive positive acetylcholinesterase nucleus basalis cholinergic neurons were observed at 2 weeks survival, while the density of acetylcholinesterase-positive fibers of cerebral cortex was increased along with the number of cortical positive neurons at 3 weeks survival. These results suggest that increased cholinergic function may be responsible of muscarinic receptor down-regulation. Given the involvement of cholinergic systems in memory and learning, repeated administration of betaA(25-35) may represent a good approach to explore the role of betaA in Alzheimer's disease and to develop therapeutic strategies relevant to it.

A beta and perlecan in rat brain: glial activation, gradual clearance and limited neurotoxicity

A beta1-40 and perlecan (A beta + perlecan) were infused into rat hippocampus for 1 week via osmotic pumps. At the end of the infusion a deposit of A beta immunoreactive material was found surrounding the infusion site. No neurons could be identified within this A beta deposit. The neuron-free area resulting from A beta + perlecan was significantly larger than that found after infusions of A beta40-1 and perlecan (reverse A beta + perlecan), perlecan alone or phosphate-buffered saline vehicle. Following infusion of A beta + perlecan, the glial cells segregated in a manner similar to that associated with compacted amyloid plaques in Alzheimer's disease (AD). Activated microglia/macrophages were prevalent within the A beta deposit while the perimeter of the deposit was delimited by reactive astrocytes. Thioflavin S and Congo red staining indicated a beta-pleated sheet conformation of the A beta deposits, implying formation of fibrils. Intact, apparently healthy neurons were found immediately adjacent to the A beta + perlecan deposit. In contrast, reverse A beta peptide did not form congophilic deposits despite the presence of perlecan. Apoptotic profiles visualized with bisbenzamide or TUNEL staining of fragmented DNA were not seen at any of the infusion sites, yet were readily seen in hippocampal sections from animals treated with kainic acid. At 8 weeks, A beta immunoreactivity, Thioflavin S and Congo red staining was reduced, indicating that A beta was being cleared. There also was no evidence of neuron loss by Nissl or TUNEL staining. The zone of apparent necrosis did not expand between 1 and 8 weeks, and in some instances appeared to contract. The consistency of the A beta + perlecan infusion method in producing reliable A beta amyloid deposits permits estimates of the rate at which fibrillar A beta amyloid can be removed from the brain, and may provide a useful model to study this process in vivo. However, the absence of clearly identifiable degenerating/dying neurons at the 1 or 8 week survival times suggests that either fibrillar A beta + perlecan slowly displaced the brain parenchyma during infusion, or neurons were killed very gradually during the process of clearing the A beta.

Uptake, degradation, and release of fibrillar and soluble forms of Alzheimer's amyloid beta-peptide by microglial cells

Microglia are phagocytic cells that are the main inflammatory response cells of the central nervous system. In Alzheimer's disease brain, activated microglia are concentrated in regions of compact amyloid deposits that contain the 39-43-amino acid Abeta peptide. We examined the uptake, degradation, and release of small aggregates of fibrillar Abeta (fAbeta) or soluble Abeta (sAbeta) by microglia. We found that although some degradation of fAbeta was observed over 3 days, no further degradation was observed over the next 9 days. Instead, there was a slow release of intact Abeta. The poor degradation was not due to inhibition of lysosomal function, since the rate of alpha2-macroglobulin degradation was not affected by the presence of fAbeta in the late endosomes/lysosomes. In contrast to fAbeta, internalization of sAbeta was not saturable. After internalization, sAbeta was released rapidly from microglia, and very little was degraded. These data show that fAbeta and sAbeta interact differently with microglia but that after internalization a large fraction of both are released without degradation.

Reduction in somatostatin and substance P levels and choline acetyltransferase activity in the cortex and hippocampus of the rat after chronic intracerebroventricular infusion of beta-amyloid (1-40)

The present study investigated the neurochemical and behavioural sequelae following chronic intracerebroventricular infusion of beta-amyloid (1-40) in rats. beta-amyloid was either infused intermittently via implanted cannulae on the day of operation and subsequently on postsurgical days 4, 7, 10, and 13 (Experiment 1), or continuously using osmotic pumps for 14 days (Experiment 2). The same amount of beta-amyloid was delivered under both infusion regimes. In both experiments, beta-amyloid infusion led to severe deficits in the acquisition of a spatial reference memory task conducted on postoperative days 10 to 14. The animals were sacrificed on the postoperative day 15 for neurochemical analyses. These included radioenzymatic and radioimmunoassays, designed to determine choline acetyltransferase activity and the contents of neuropeptides (somatostatin, substance P, and neuropeptide Y), respectively. Experiment 2 also included solution-hybridisation-RNAase protection assay for preprosomatostatin mRNA quantification. There was a significant reduction in choline acetyltransferase activity and in the levels of substance P as well as somatostatin and preprosomatostatin mRNA in the cortical mantle of beta-amyloid-treated rats, compared to controls in both experiments. Appreciable reductions in choline acetyltransferase activity and somatostatin level were also apparent in the hippocampus. In contrast, beta-amyloid infusion did not significantly affect the brain level of neuropeptide Y. The present study demonstrated that chronic infusion of beta-amyloid can lead to a reduction in the levels of selected neuropeptides resembling the pattern seen in Alzheimer's disease patients.

Impairments of long-term potentiation in hippocampal slices of beta-amyloid-infused rats

In this study, we investigated the neuronal activity of hippocampal slices from the beta-amyloid protein-infused (300 pmol/day for 10-11 days) rats using the extracellular recording technique. Perfusion of nicotine (50 microM) reduced the amplitude of electrically evoked population spikes in the CA1 pyramidal cells of the vehicle control rats, but not in those of the beta-amyloid protein-infused rats, suggesting the impairment of nicotinic signaling in the beta-amyloid protein-infused rats. Long-term potentiation induced by tetanic stimulations in CA1 pyramidal cells, which was readily observed in the vehicle control rats, was also impaired in the beta-amyloid protein-infused rats. Nicotinic blockade by adding hexamethonium into the perfused solution inhibited long-term potentiation induction. Taken together, our previous and present results suggest that beta-amyloid protein infusion impairs the signal transduction mechanisms via nicotinic acetylcholine receptors. This dysfunction may be responsible, at least in part, for the impairment of long-term potentiation induction and may lead to learning deficits.

Protease inhibitor coinfusion with amyloid beta-protein results in enhanced deposition and toxicity in rat brain

Amyloid beta-protein, Abeta, is normally produced in brain and is cleared by unknown mechanisms. In Alzheimer's disease (AD), Abeta accumulates in plaque-like deposits and is implicated genetically in neurodegeneration. Here we investigate mechanisms for Abeta degradation and Abeta toxicity in vivo, focusing on the effects of Abeta40, which is the peptide that accumulates in apolipoprotein E4-associated AD. Chronic intraventricular infusion of Abeta40 into rat brain resulted in limited deposition and toxicity. Coinfusion of Abeta40 with the cysteine protease inhibitor leupeptin resulted in increased extracellular and intracellular Abeta immunoreactivity. Analysis of gliosis and TUNEL in neuron layers of the frontal and entorhinal cortex suggested that leupeptin exacerbated Abeta40 toxicity. This was supported further by the neuronal staining of cathepsin B in endosomes or lysosomes, colocalizing with intracellular Abeta immunoreactivity in pyknotic cells. Leupeptin plus Abeta40 caused limited but significant neuronal phospho-tau immunostaining in the entorhinal cortex. Intriguingly, Abeta40 plus leupeptin induced intracellular accumulation of the more toxic Abeta, Abeta42, in a small group of septal neurons. Leupeptin infusion previously has been reported to interfere with lysosomal proteolysis and to result in the accumulation of lipofuscin, dystrophic neurites, tau- and ubiquitin-positive inclusions, and structures resembling paired helical filaments. Coinfusion of Abeta40 with the serine protease inhibitor aprotinin also increased diffuse extracellular deposition but reduced astrocytosis and TUNEL and was not associated with intracellular Abeta staining. Collectively, these data suggest that an age or Alzheimer's-related defect in lysosomal/endosomal function could promote Abeta deposition and DNA fragmentation in neurons and glia similar to that found in Alzheimer's disease.

Vulnerability of small GABAergic neurons to human beta-amyloid pentapeptide

beta-Amyloid peptide (A beta), the principal component of senile plaques in Alzheimer's disease, has been found to be neurotoxic. The role of A beta in the deficits of the GABAergic system in patients with Alzheimer's disease is unclear. It has been suggested that the cytotoxic activity of A beta is localized to amino acid residues 25-35 of this peptide, which contains a total of 42 amino acid residues. We now report that the short amyloid peptide fragments corresponding to amino acids 31-35 (A beta 31-35) and 34-39 (A beta 34-39) are also toxic in vitro to the small GABAergic neuron population of basal forebrain cultures. Morphological changes were accompanied by an increased number of varicosities localized on the processes of the GABA-immunoreactive neurons and by the appearance of round cells without processes. The neurodegeneration was confirmed by means of scanning electron microscopy. Quantification of the morphological findings by image analysis demonstrated a size-related dependence of the degeneration of GABAergic neurons. The results suggest that fragments of A beta shorter than A beta 25-35 may exert cytotoxic action and demonstrate the toxicity of these A beta fragments in decreasing the number of small GABAergic neurons.

Amyloid beta-protein (Abeta) 1-40 but not Abeta1-42 contributes to the experimental formation of Alzheimer disease amyloid fibrils in rat brain

Two major C-terminal variants ending at Val40 and Ala42 constitute the majority of amyloid beta-protein (Abeta), which undergoes postsecretory aggregation and deposition in the Alzheimer disease (AD) brain. To probe the differential pathobiology of the two Abeta variants, we used an in vivo paradigm in which freshly solubilized Abeta1-40 or Abeta1-42 was injected into rat brains, followed by examination using Congo red birefringence, Abeta immunohistochemistry, and electron microscopy. In the rat brain, soluble Abeta 1-40 and Abeta1-42 formed aggregates, and the Abeta1-40 but not the Abeta1-42 aggregates showed Congo red birefringence. Electron microscopy revealed that the Abeta1-40 aggregates contained fibrillar structures similar to the amyloid fibrils of AD, whereas the Abeta1-42 aggregates contained nonfibrillar amorphous material. Preincubation of Abeta1-42 solution in vitro led to the formation of birefringent aggregates, and after injection of the preincubated Abeta1-42, the aggregates remained birefringent in the rat brain. Thus, a factor or factors might exist in the rat brain that inhibit the fibrillar assembly of soluble Abeta1-42. To analyze the postsecretory processing of Abeta, we used the same in vivo paradigm and showed that Abeta1-40 and Abeta1-42 were processed at their N termini to yield variants starting at pyroglutamate, and at their C termini to yield variants ending at Val40 and at Val39. Thus the normal rat brain could produce enzymes that mediate the conversion of Abeta 1-40/1-42 into processed variants similar to those in AD. This experimental paradigm may facilitate efforts to elucidate mechanisms of Abeta deposition evolving into amyloid plaques in AD.

Pharmaceutical applications of cyclodextrins. III. Toxicological issues and safety evaluation

The objective of this review is to summarize recent findings on the safety profiles of three natural cyclodextrins (alpha-, beta- and gamma-CDs) and several chemically modified CDs. To demonstrate the potential of CDs in pharmaceutical formulations, their stability against non-enzymatic and enzymatic degradations in various body fluids and tissue homogenates and their pharmacokinetics via parenteral, oral, transmucosal, and dermal routes of administration are outlined. Furthermore, the bioadaptabilities of CDs, including in vitro cellular interactions and in vivo safety profiles, via a variety of administration routes are addressed. Finally, the therapeutic potentials of CDs are discussed on the basis of their ability to interact with various endogenous and exogenous lipophiles or, especially for sulfated CDs, their effects on cellular processes mediated by heparin binding growth factors.

Permeability and residual plasma volume of human, Dutch variant, and rat amyloid beta-protein 1-40 at the blood-brain barrier

The permeability of normal human, the human Dutch variant, and the rat A beta 1-40 proteins at the blood-brain barrier (BBB) was determined in the normal adult rat by quantifying the permeability coefficient-surface area (PS) product for each protein after correction for the residual plasma volume (Vp) occupied by the protein in the blood vessels of different brain regions. The PS for normal and Dutch A beta ranged from 13 x 10(-6) to 22 x 10(-6) ml/g/s in different brain regions, which is 130 to 220 times greater than albumin. These high PS values compare to that of insulin, whose uptake is decidedly by a receptor-mediated transport process, and suggest a similar mechanism for A beta. Remarkably, the PS for rat A beta was 4 times higher and ranged from 54 x 10(-6) to 82 x 10(-6) ml/g/s for different brain regions, suggesting a distinctive species specificity. While the Vp values of human and rat A beta were comparable, the Dutch variant was 2 to 3 times higher, indicating adherence to the vessel walls in different brain regions, consistent with the heavy A beta deposition that has been described in intracerebral vessel walls with this variant. The high PS values observed for A beta at the BBB suggest that sources outside the nervous system could contribute, at least in part, to the cerebral A beta deposits seen in Alzheimer's disease. SDS-PAGE of 125I-labeled human A beta after 60 min of uptake revealed intact protein in plasma and in different brain regions. In addition, 125I-labeled human A beta binding to a protein of 67,000 in both plasma and brain tissue regions was observed with SDS-PAGE. This protein was tentatively identified as albumin, and it was not detectable in the brain regions of animals that had undergone intracardiac perfusion; hence, a portion of A beta binds tightly to and is likely transported by albumin in plasma. The absence of this A beta-albumin complex in brain regions after perfusion and the low permeability of albumin at the BBB imply that A beta itself is efficiently transported at the BBB to account for the high PS values, although presentation of A beta to the capillary endothelial cell by albumin or other plasma proteins cannot be excluded.

Transforming growth factors-beta protect primary rat hippocampal neuronal cultures from degeneration induced by beta-amyloid peptide

Treatment of primary rat embryo hippocampal neuronal cultures with 10(-5) M beta-amyloid peptide fragment 25-35 (A beta P) for 24 h resulted in a 60% decrease in cell viability as determined by MTT incorporation. When these cells were treated with 0.1-10 ng/ml of either transforming growth factor-beta (TGF-beta) 1, 2 or 3 for 24 h before exposure to A beta P, there was a 2.9-, 1.9-, and 3.2-fold increase in cell survival, respectively, compared to cells treated with A beta P alone. The viability of cells treated with A beta P and 0.1-10 ng/ml TGF-beta was comparable to that of cells not treated with A beta P. The protective effects were less pronounced at lower TGF-beta concentrations. The protective effects of pretreatment with TGF-beta were less striking in mouse CCL-N-2a and human SK-N-SH neuroblastoma cell lines. When all cells were treated with TGF-beta for 24 h following a 24 h exposure to A beta P, there was a trend toward increased cell viability which was less significant than pretreatment with TGFs-beta. An isoform-specific TGF-beta SELISA showed that primary hippocampal neuronal cultures and the neuroblastoma cell lines secrete all 3 TGF-beta isoforms. Based on our results, we propose that the increased expression of TGF-beta observed in brains of patients with Alzheimer's disease may offer some degree of neuroprotection.

Effects of chronic beta-amyloid treatment on fatty acid incorporation into rat brain

The present study evaluated the effects of chronic A beta administration on radio-labeled plasma fatty acid incorporation in rat brain. A beta was chronically infused intraventricularly via an osmotic minipump, for 1 week, at a concentration of 460 microM. After the infusion, fatty acid incorporation was quantified using an in vivo method developed in this laboratory. Three radiolabeled fatty acids were separately infused IV in awake animals. Biochemical analyses of fatty acid incorporation and histology for A beta showed no differences between control (vehicle infusion only) and experimental groups. However, in vitro tests on the cytotoxicity of A beta showed that it caused significant cell death relative to controls (PC-12 cells). The lack of effect of infused A beta on radiolabeled fatty acid incorporation is discussed.

Rodent models of Alzheimer's disease: rat A beta infusion approaches to amyloid deposits

The development of rodent models for Alzheimer's disease is a critical step for both understanding the disease and developing therapeutic drugs. Transgenic and knockout mouse models will elucidate some important aspects of the etiology of the disease and the development of pharmaceutical treatments. Here, we will focus on the advantages of nontransgenic models. In nontransgenic rat models, intraventricular infusion of A beta 1-40 (alone) generally results in diffuse deposition of A beta with very few focal plaque-like amyloid deposits after a 30-day intraventricular infusion. However, we have recently found that large numbers of scattered A beta immunoreactive plaque-like deposits can be produced in retired female Sprague-Dawley rat breeders using intraventricular infusion of A beta combined with neuropil injection of transforming growth factor beta 1(TGF beta). A beta that was not associated with the large deposits was often immunolocalized with neurons and cell processes. Immunogold electron microscopy demonstrated the presence of A beta in endosome/lysosomes of neuronal processes and glia and basal lamina. In some cases this labeling was clearly in lysosomes of degenerating neurites. This model allows one to introduce A beta and other plaque-associated factors without overexpression of potentially confounding APP domains. We conclude that A beta infusion models will be a useful complement to transgenic approaches to Alzheimer's pathology.

Amnesia induced in mice by centrally administered beta-amyloid peptides involves cholinergic dysfunction

Substantial evidences suggest that the increased cerebral deposition, and neurotoxic action of the beta-amyloid peptide, the major constituent of senile plaques, may represent the underlying cause of the cognitive deficits observed in Alzheimer's disease. Herein, we attempted to verify this hypothesis by inducing a potential Alzheimer's-type amnesia after direct intracerebroventricular administration of aggregated beta 25-35-amyloid peptide in mice. In this aim, mnesic capacities were evaluated after 6-13 days, using spontaneous alternation in the Y-maze, step-down type passive avoidance and place learning in a water-maze. Pretraining administration of aggregated beta 25-35 peptide induced dose-dependent decreases in both alternation behaviour and passive avoidance, at doses of 3 and 9 nmol/mouse. A reduced but still significant impairment was observed when the peptide was not aggregated, or 'aged', by preincubation for 4 days at 37 degrees C. The beta 1-28 peptide, at 3 nmol/mouse, also induced a marked decrease in step-down latency. Posttraining, but not preretention, administration of beta 25-35 peptide also significantly impaired learning. The beneficial effects of cholinergic agents on beta 25-35-induced amnesia was examined using the cholinesterase inhibitor tacrine (THA, 1.3 and 4.3 mumol/kg i.p.) and the nicotinic receptor agonist (-)-nicotine (NIC, 0.06 and 0.2 mumol/kg i.p.). Both drugs induced a dose-dependent abrogation of the beta 25-35-induced decreases in alternation behaviour and passive avoidance. Furthermore, THA, at 1.3 mumol/kg, and NIC, at 0.2 mumol/kg, also reversed the beta 25-35-induced impairment of place learning and retention in the water-maze. Histological examination of Cresyl violet-stained brain sections indicated a moderate but significant cell loss within the frontoparietal cortex and the hippocampal formation of mice treated with aged beta 25-35 peptide (9 nmol). Examination of Congo red-stained sections in the same animals demonstrated the presence of numerous amyloid deposits throughout these brain areas. These results confirm that the deposition of beta-amyloid peptide in the brain is in some way related to impairment of learning and cholinergic degeneration and suggest that the [25-35] fragment of the beta-amyloid protein, sufficient to induce neuronal death in cultures, also induces an Alzheimer's-type amnesia in mice.