Identification of the major Abeta1-42-degrading catabolic pathway in brain parenchyma: suppression leads to biochemical and pathological deposition

Alzheimer amyloid beta-peptide (Abeta) is a physiological peptide constantly anabolized and catabolized under normal conditions. We investigated the mechanism of catabolism by tracing multiple-radiolabeled synthetic peptide injected into rat hippocampus. The Abeta1-42 peptide underwent full degradation through limited proteolysis conducted by neutral endopeptidase (NEP) similar or identical to neprilysin as biochemically analyzed. Consistently, NEP inhibitor infusion resulted in both biochemical and pathological deposition of endogenous Abeta42 in brain. This NEP-catalyzed proteolysis therefore limits the rate of Abeta42 catabolism, up-regulation of which could reduce the risk of developing Alzheimer's disease by preventing Abeta accumulation.     

Susceptibility of amyloid beta peptide degrading enzymes to oxidative damage: a potential Alzheimer's disease spiral

Insulysin (IDE) and neprilysin (NEP) were found to be inactivated by oxidation with hydrogen peroxide, an iron-ascorbate oxidation system, and by treatment with 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH). In each case reaction led to the introduction of protein carbonyl groups as judged by reaction with 2,4-dintrophenylhydrazine. IDE was inactivated by reaction with 4-hydroxy-2-nonenal (HNE) with the concomitant formation of protein adducts. NEP was not inactivated to a significant extent by HNE, but some HNE-adduct formation did occur. Prior reaction with hydrogen peroxide or AAPH led to enhanced formation of HNE adducts. Treatment of IDE with AAHP or hydrogen peroxide increased its susceptibility to proteolysis, while treatment of NEP with iron/ascorbate or hydrogen peroxide increased its susceptibility to proteolysis. Since IDE and NEP play a prominent role in the clearance of amyloid beta peptides, their oxidative inactivation and enhanced proteolysis can contribute to the onset and/or progression of Alzheimer's disease.     

Fibrillar amyloid-beta peptides activate microglia via TLR2: implications for Alzheimer's disease

Microglial activation is an important pathological component in brains of patients with Alzheimer's disease (AD), and fibrillar amyloid-beta (Abeta) peptides play an important role in microglial activation in AD. However, mechanisms by which Abeta peptides induce the activation of microglia are poorly understood. The present study underlines the importance of TLR2 in mediating Abeta peptide-induced activation of microglia. Fibrillar Abeta1-42 peptides induced the expression of inducible NO synthase, proinflammatory cytokines (TNF-alpha, IL-1beta, and IL-6), and integrin markers (CD11b, CD11c, and CD68) in mouse primary microglia and BV-2 microglial cells. However, either antisense knockdown of TLR2 or functional blocking Abs against TLR2 suppressed Abeta1-42-induced expression of proinflammatory molecules and integrin markers in microglia. Abeta1-42 peptides were also unable to induce the expression of proinflammatory molecules and increase the expression of CD11b in microglia isolated from TLR2(-/-) mice. Finally, the inability of Abeta1-42 peptides to induce the expression of inducible NO synthase and to stimulate the expression of CD11b in vivo in the cortex of TLR2(-/-) mice highlights the importance of TLR2 in Abeta-induced microglial activation. In addition, ligation of TLR2 alone was also sufficient to induce microglial activation. Consistent to the importance of MyD88 in mediating the function of various TLRs, antisense knockdown of MyD88 also inhibited Abeta1-42 peptide-induced expression of proinflammatory molecules. Taken together, these studies delineate a novel role of TLR2 signaling pathway in mediating fibrillar Abeta peptide-induced activation of microglia.     

Oxidized neprilysin in aging and Alzheimer's disease brains

Deposition of amyloid in the brain is important in the pathogenesis of Alzheimer's disease (AD), but it remains to be determined if deposition is due to increased production or decreased clearance of fibrillogenic forms of beta-amyloid (Abeta). Except for rare genetic forms of AD, there is little evidence for increased production of Abeta, but decreases in enzymes involved in the clearance of Abeta are increasingly being investigated. Neprilysin (NEP) is a major enzyme for degradation of Abeta and changes in amount or activity of NEP may play a role in Abeta deposition in AD. Since oxidative damage to proteins, including formation of adducts such as 4-hydroxynonenal (HNE), has been reported in AD, it was of interest to determine if NEP might be susceptible to oxidative modification. To address this question, monoclonal antibody immunoprecipitates of NEP were probed with polyclonal antibodies to NEP and HNE. The results showed decreased NEP in AD compared to normal controls. NEP in both AD and controls had HNE-modification and the ratio of oxidized to total NEP was greater in AD than in controls. These findings suggest that decreased NEP may contribute to Abeta deposition in AD and that age-related oxidative damage to NEP may play a role in age-related cerebral amyloidosis that is exacerbated in AD.     

Cytokine-mediated inhibition of fibrillar amyloid-beta peptide degradation by human mononuclear phagocytes

Vaccination therapy of AD animal models and patients strongly suggests an active role of brain mononuclear phagocytes in immune-mediated clearance of amyloid-beta peptides (Abeta) in brain. Although Abeta uptake by macrophages can be regulated by pro- and anti-inflammatory cytokines, their effects on macrophage-mediated Abeta degradation are poorly understood. To better understand this mechanism of degradation, we examined whether pro- and anti-inflammatory cytokines affect the degradation of Abeta using primary cultured human monocyte-derived macrophages (MDM) and microglia using pulse-chase analysis of fibrillar and oligomer (125)I-Abeta40 and Abeta42. Initial uptake of fibrillar Abeta40 and Abeta42 was 40% and its degradation was saturated by 120 h in both MDM and microglia, compared with an initial uptake of oligomeric Abeta less than 0.5% and saturation of degradation within 24 h. IFN-gamma increased the intracellular retention of fibrillar Abeta40 and Abeta42 by inhibiting degradation, whereas IL-4, IL-10, and TGF-beta1, but not IL-13 and IL-27, enhanced degradation. Fibrillar Abeta degradation in MDM is sensitive to lysosomal and insulin degrading enzyme inhibitors but insensitive to proteasomal and neprilysin inhibitors. IFN-gamma and TNF-alpha directly reduced the expression of insulin degrading enzyme and chaperone molecules (heat shock protein 70 and heat shock cognate protein 70), which are involved in refolding of aggregated proteins. Coculture of MDM with activated, but not naive T cells, suppressed Abeta degradation in MDM, which was partially blocked by a combination of neutralizing Abs against proinflammatory cytokines. These data suggest that proinflammatory cytokines suppress Abeta degradation in MDM, whereas select anti-inflammatory and regulatory cytokines antagonize these effects.     

Differential effects of proteases involved in intracellular degradation of amyloid beta-protein between detergent-soluble and -insoluble pools in CHO-695 cells.

The deposition of amyloid beta-protein (A beta or beta A4) is a key feature of Alzheimer's disease. Most studies have focused on the generation of A beta, but little is known about the degradation of A beta. Recent reports suggest that insulin-degrading enzyme (IDE) and neutral endopeptidase (NEP) are involved in the extracellular degradation of A beta. To date, however, far less is known about the degradation of intracellular A beta. To elucidate the protease(s) responsible for the degradation of intracellular A beta, we investigated the effect of various protease inhibitors on A beta in two distinct intracellular pools (i.e., nonionic detergent-soluble and detergent-insoluble pools) in Chinese hamster ovary cells. Treatment with thiol and metal inhibitors resulted in the accumulation of intracellular A beta and oligomers in detergent-soluble and -insoluble fractions. The overexpression of thiol-metalloprotease IDE resulted in a marked reduction in levels of detergent-soluble intracellular A beta as well as extracellular A beta 40 and A beta 42. Moreover, intracellular A beta in the detergent-insoluble fraction extracted with 70% formic acid or 6 M guanidine hydrochloride decreased markedly in the cells overexpressing IDE. In contrast, expression of NEP degraded the A beta in the detergent-insoluble fraction markedly and partially degraded extracellular A beta 40 and A beta 42, but not intracellular soluble A beta. Thiorphan, an inhibitor of NEP, accumulated, albeit to a lesser extent, in insoluble A beta but not in soluble A beta. Thus, IDE appears to degrade intracellular A beta more effectively than does NEP in both the detergent-soluble and -insoluble fractions.     

Enhanced proteolysis of beta-amyloid in APP transgenic mice prevents plaque formation, secondary pathology, and premature death

Converging evidence suggests that the accumulation of cerebral amyloid beta-protein (Abeta) in Alzheimer's disease (AD) reflects an imbalance between the production and degradation of this self-aggregating peptide. Upregulation of proteases that degrade Abeta thus represents a novel therapeutic approach to lowering steady-state Abeta levels, but the consequences of sustained upregulation in vivo have not been studied. Here we show that transgenic overexpression of insulin-degrading enzyme (IDE) or neprilysin (NEP) in neurons significantly reduces brain Abeta levels, retards or completely prevents amyloid plaque formation and its associated cytopathology, and rescues the premature lethality present in amyloid precursor protein (APP) transgenic mice. Our findings demonstrate that chronic upregulation of Abeta-degrading proteases represents an efficacious therapeutic approach to combating Alzheimer-type pathology in vivo.     

Insulin-degrading enzyme in brain microvessels: proteolysis of amyloid {beta} vasculotropic variants and reduced activity in cerebral amyloid angiopathy

The accumulation of amyloid beta (Abeta) in the walls of small vessels in the cerebral cortex is associated with diseases characterized by dementia or stroke. These include Alzheimer's disease, Down syndrome, and sporadic and hereditary cerebral amyloid angiopathies (CAAs) related to mutations within the Abeta sequence. A higher tendency of Abeta to aggregate, a defective clearance to the systemic circulation, and insufficient proteolytic removal have been proposed as mechanisms that lead to Abeta accumulation in the brain. By using immunoprecipitation and mass spectrometry, we show that insulin-degrading enzyme (IDE) from isolated human brain microvessels was capable of degrading (125)I-insulin and cleaved Abeta-(1-40) wild type and the genetic variants Abeta A21G (Flemish), Abeta E22Q (Dutch), and Abeta E22K (Italian) at the predicted sites. In microvessels from Alzheimer's disease cases with CAA, IDE protein levels showed a 44% increase as determined by sandwich enzyme-linked immunosorbent assay and Western blot. However, the activity of IDE upon radiolabeled insulin was significantly reduced in CAA as compared with age-matched controls. These results support the notion that a defect in Abeta proteolysis by IDE contributes to the accumulation of this peptide in the cortical microvasculature. Moreover they raise the possibility that IDE inhibition or inactivation is a pathogenic mechanism that may open novel strategies for the treatment of cerebrovascular Abeta amyloidoses.     

β‐Amyloid catabolism: roles for neprilysin (NEP) and other metallopeptidases?

The steady-state level of amyloid beta-peptide (Abeta) represents a balance between its biosynthesis from the amyloid precursor protein (APP) through the action of the beta- and gamma-secretases and its catabolism by a variety of proteolytic enzymes. Recent attention has focused on members of the neprilysin (NEP) family of zinc metalloproteinases in amyloid metabolism. NEP itself degrades both Abeta(1-40) and Abeta(1-42) in vitro and in vivo, and this metabolism is prevented by NEP inhibitors. Other NEP family members, for example endothelin-converting enzyme, may contribute to amyloid catabolism and may also play a role in neuroprotection. Another metalloproteinase, insulysin (insulin-degrading enzyme) has also been advocated as an amyloid-degrading enzyme and may contribute more generally to metabolism of amyloid-forming peptides. Other candidate enzymes proposed include angiotensin-converting enzyme, some matrix metalloproteinases, plasmin and, indirectly, thimet oligopeptidase (endopeptidase-24.15). This review critically evaluates the evidence relating to proteinases implicated in amyloid catabolism. Therapeutic strategies aimed at promoting A,beta degradation may provide a novel approach to the therapy of Alzheimer's disease.     

Heterologous amyloid seeding: revisiting the role of acetylcholinesterase in Alzheimer's disease

Neurodegenerative diseases associated with abnormal protein folding and ordered aggregation require an initial trigger which may be infectious, inherited, post-inflammatory or idiopathic. Proteolytic cleavage to generate vulnerable precursors, such as amyloid-beta peptide (Abeta) production via beta and gamma secretases in Alzheimer's Disease (AD), is one such trigger, but the proteolytic removal of these fragments is also aetiologically important. The levels of Abeta in the central nervous system are regulated by several catabolic proteases, including insulysin (IDE) and neprilysin (NEP). The known association of human acetylcholinesterase (hAChE) with pathological aggregates in AD together with its ability to increase Abeta fibrilization prompted us to search for proteolytic triggers that could enhance this process. The hAChE C-terminal domain (T40, AChE(575-614)) is an exposed amphiphilic alpha-helix involved in enzyme oligomerisation, but it also contains a conformational switch region (CSR) with high propensity for conversion to non-native (hidden) beta-strand, a property associated with amyloidogenicity. A synthetic peptide (AChE(586-599)) encompassing the CSR region shares homology with Abeta and forms beta-sheet amyloid fibrils. We investigated the influence of IDE and NEP proteolysis on the formation and degradation of relevant hAChE beta-sheet species. By combining reverse-phase HPLC and mass spectrometry, we established that the enzyme digestion profiles on T40 versus AChE(586-599), or versus Abeta, differed. Moreover, IDE digestion of T40 triggered the conformational switch from alpha- to beta-structures, resulting in surfactant CSR species that self-assembled into amyloid fibril precursors (oligomers). Crucially, these CSR species significantly increased Abeta fibril formation both by seeding the energetically unfavorable formation of amyloid nuclei and by enhancing the rate of amyloid elongation. Hence, these results may offer an explanation for observations that implicate hAChE in the extent of Abeta deposition in the brain. Furthermore, this process of heterologous amyloid seeding by a proteolytic fragment from another protein may represent a previously underestimated pathological trigger, implying that the abundance of the major amyloidogenic species (Abeta in AD, for example) may not be the only important factor in neurodegeneration.     

Biogenesis and metabolism of Alzheimer's disease Abeta amyloid peptides

Biochemical and genetic evidence indicates the balance of biogenesis/clearance of Abeta amyloid peptides is altered in Alzheimer's disease. Abeta is derived, by two sequential cleavages, from the receptor-like amyloid precursor protein (APP). The proteases involved are beta-secretase, identified as the novel aspartyl protease BACE, and gamma-secretase, a multimeric complex containing the presenilins (PS). Gamma-secretase can release either Abeta40 or the more aggregating and cytotoxic Abeta42. Secreted Abeta peptides become either degraded by the metalloproteases insulin-degrading enzyme (IDE) and neprilysin or metabolized through receptor uptake mediated by apolipoprotein E. Therapeutic approaches based on secretase inhibition or amyloid clearance are currently under development.     

Ferulic acid ethyl ester protects neurons against amyloid beta- peptide(1-42)-induced oxidative stress and neurotoxicity: relationship to antioxidant activity

Alzheimer's disease (AD) is neuropathologically characterized by depositions of extracellular amyloid and intracellular neurofibrillary tangles, associated with loss of neurons in the brain. Amyloid beta-peptide (Abeta) is the major component of senile plaques and is considered to have a causal role in the development and progress of AD. Several lines of evidence suggest that enhanced oxidative stress and inflammation play important roles in the pathogenesis or progression of AD. The present study aimed to investigate the protective effects of ethyl-4-hydroxy-3-methoxycinnamic acid (FAEE), a phenolic compound which shows antioxidant and anti-inflammatory activity, on Abeta(1-42)-induced oxidative stress and neurotoxicity. We hypothesized that the structure of FAEE would facilitate radical scavenging and may induce protective proteins. Abeta(1-42) decreases cell viability, which was correlated with increased free radical formation, protein oxidation (protein carbonyl, 3-nitrotyrosine), lipid peroxidation (4-hydroxy-2-trans-nonenal) and inducible nitric oxide synthase. Pre-treatment of primary hippocampal cultures with FAEE significantly attenuated Abeta(1-42)-induced cytotoxicity, intracellular reactive oxygen species accumulation, protein oxidation, lipid peroxidation and induction of inducible nitric oxide synthase. Treatment of neurons with Abeta(1-42) increases levels of heme oxygenase-1 and heat shock protein 72. Consistent with a cellular stress response to the Abeta(1-42)-induced oxidative stress, FAEE treatment increases the levels of heme oxygenase-1 and heat shock protein 72, which may be regulated by oxidative stresses in a coordinated manner and play a pivotal role in the cytoprotection of neuronal cells against Abeta(1-42)-induced toxicity. These results suggest that FAEE exerts protective effects against Abeta(1-42) toxicity by modulating oxidative stress directly and by inducing protective genes. These findings suggest that FAEE could potentially be of importance for the treatment of AD and other oxidative stress-related diseases.     

Proteinase-activated receptor-2 exerts protective and pathogenic cell type-specific effects in Alzheimer's disease

The proteinase-activated receptors (PARs) are a novel family of G protein-coupled receptors, and their effects in neurodegenerative diseases remain uncertain. Alzheimer's disease (AD) is a neurodegenerative disorder defined by misfolded protein accumulation with concurrent neuroinflammation and neuronal death. We report suppression of proteinase-activated receptor-2 (PAR2) expression in neurons of brains from AD patients, whereas PAR2 expression was increased in proximate glial cells, together with up-regulation of proinflammatory cytokines and chemokines and reduced IL-4 expression (p < 0.05). Glial PAR2 activation increased expression of formyl peptide receptor-2 (p < 0.01), a cognate receptor for a fibrillar 42-aa form of beta-amyloid (Abeta(1-42)), enhanced microglia-mediated proinflammatory responses, and suppressed astrocytic IL-4 expression, resulting in neuronal death (p < 0.05). Conversely, neuronal PAR2 activation protected human neurons against the toxic effects of Abeta(1-42) (p < 0.05), a key component of AD neuropathogenesis. Amyloid precursor protein-transgenic mice, displayed glial fibrillary acidic protein and IL-4 induction (p < 0.05) in the absence of proinflammatory gene up-regulation and neuronal injury, whereas PAR2 was up-regulated at this early stage of disease progression. PAR2-deficient mice, after hippocampal Abeta(1-42) implantation, exhibited enhanced IL-4 induction and less neuroinflammation (p < 0.05), together with improved neurobehavioral outcomes (p < 0.05). Thus, PAR2 exerted protective properties in neurons, but its activation in glia was pathogenic with secretion of neurotoxic factors and suppression of astrocytic anti-inflammatory mechanisms contributing to Abeta(1-42)-mediated neurodegeneration.     

CD36 overexpression in human brain correlates with beta-amyloid deposition but not with Alzheimer's disease

Scavenger receptors recently have been related to Alzheimer's disease, although it is still unclear whether they contribute to the pathogenesis of the disease or reflect an inflammatory response to the deposition of amyloid beta-protein (Abeta). In this study we demonstrate that CD36, a class B scavenger receptor, is highly expressed in the cerebral cortex of Alzheimer's disease patients and cognitively normal aged subjects with diffuse amyloid plaques compared with age-matched amyloid-free control brains. Moreover, in vitro experiments indicated that Abeta is able to induce CD36 expression in neuronal cells after 24 h treatment. The interaction between CD36 and Abeta has been reported to trigger oxidant production by macrophages and microglia. In line with this observation, we found an increased presence of nitrated proteins in brains showing Abeta loads and CD36 overexpression, independent of the occurrence of Alzheimer's disease pathologic features.     

Differential degradation of amyloid beta genetic variants associated with hereditary dementia or stroke by insulin-degrading enzyme

Inherited amino acid substitutions at position 21, 22, or 23 of amyloid beta (Abeta) lead to presenile dementia or stroke. Insulin-degrading enzyme (IDE) can hydrolyze Abeta wild type, yet whether IDE is capable of degrading Abeta bearing pathogenic substitutions is not known. We studied the degradation of all of the published Abeta genetic variants by recombinant rat IDE (rIDE). Monomeric Abeta wild type, Flemish (A21G), Italian (E22K), and Iowa (D23N) variants were readily degraded by rIDE with a similar efficiency. However, proteolysis of Abeta Dutch (E22Q) and Arctic (E22G) was significantly lower as compared with Abeta wild type and the rest of the mutant peptides. In the case of Abeta Dutch, inefficient proteolysis was related to a high content of beta structure as assessed by circular dichroism. All of the Abeta variants were cleaved at Glu3-Phe4 and Phe4-Arg5 in addition to the previously described major sites within positions 13-15 and 18-21. SDS-stable Abeta dimers were highly resistant to proteolysis by rIDE regardless of the variant, suggesting that IDE recognizes a conformation that is available for interaction only in monomeric Abeta. These results raise the possibility that upregulation of IDE may promote the clearance of soluble Abeta in hereditary forms of Abeta diseases.     

Amyloid precursor protein (APP) and the biology of proteolytic processing: relevance to Alzheimer's disease

The processing of amyloid precursor protein (APP) generates amyloid-beta (Abeta) peptides 1-40 and 1-42. The latter is neurotoxic and its accumulation results in amyloid fibril formation and the generation of senile plaques, the hallmark of Alzheimer's disease (AD). Whilst there has been considerable progress made in understanding the generation of Abeta by alpha-, beta- and gamma-secretase activity on APP, recently enzymes involved in the degradation of Abeta have been identified including neprilysin and insulin-degrading enzyme (IDE). We review the pathways involved in proteolytic processing of APP and discuss the potential implications of aberrant proteolysis on neurodegeneration. It is conceivable that single nucleotide polymorphisms (SNPs) in the regulatory regions of genes in these proteolytic cascades, which alter their expression, could contribute to some of the age-related changes seen in AD.     

Epigallocatechin-3-gallate suppresses NF-kappaB activation and phosphorylation of p38 MAPK and JNK in human astrocytoma U373MG cells

Epigallocatechin-3-gallate (EGCG) is the major polyphenol component of green tea and is primarily responsible for the green tea effect. EGCG possesses two triphenolic groups in its structure. These groups are reported to be important with respect to anticarcinogenic and antioxidant effects. However, the anti-inflammatory effect of EGCG on Alzheimer's disease (AD) is still not fully understood. In this study, we investigated the effects of EGCG in attenuating the inflammatory response induced by interleukin (IL)-1beta+beta-amyloid (25-35) fragment (Abeta) in human astrocytoma, U373MG cells. EGCG significantly inhibited the IL-1beta+Abeta (25-35)-induced IL-6, IL-8, vascular endothelial growth factor (VEGF) and prostaglandin (PG)E(2) production at 24 h (P<.01). The maximal inhibition rate of IL-6, IL-8, VEGF and PGE(2) production by EGCG was approximately 54.40%, 56.01%, 69.06% and 47.03%, respectively. EGCG also attenuated the expression of cyclooxygenase-2 and activation of nuclear factor-kappaB induced by IL-1beta+Abeta (25-35). We demonstrated that EGCG suppresses IL-1beta+Abeta (25-35)-induced phosphorylation of the mitogen-activated protein kinase p38 and the c-Jun N-terminal kinase. In addition, EGCG induced the expression of mitogen-activated protein kinase phosphatase-1. These results provide new insight into the pharmacological actions of EGCG and its potential therapeutic application to various neurodegenerative diseases such as AD.     

Amyloid beta-protein (Abeta)1-40 protects neurons from damage induced by Abeta1-42 in culture and in rat brain

Previously, we found that amyloid beta-protein (Abeta)1-42 exhibits neurotoxicity, while Abeta1-40 serves as an antioxidant molecule by quenching metal ions and inhibiting metal-mediated oxygen radical generation. Here, we show another neuroprotective action of nonamyloidogenic Abeta1-40 against Abeta1-42-induced neurotoxicity in culture and in vivo. Neuronal death was induced by Abeta1-42 at concentrations higher than 2 microm, which was prevented by concurrent treatment with Abeta1-40 in a dose-dependent manner. However, metal chelators did not prevent Abeta1-42-induced neuronal death. Circular dichroism spectroscopy showed that Abeta1-40 inhibited the beta-sheet transformation of Abeta1-42. Thioflavin-T assay and electron microscopy analysis revealed that Abeta1-40 inhibited the fibril formation of Abeta1-42. In contrast, Abeta1-16, Abeta25-35, and Abeta40-1 did not inhibit the fibril formation of Abeta1-42 nor prevent Abeta1-42-induced neuronal death. Abeta1-42 injection into the rat entorhinal cortex (EC) caused the hyperphosphorylation of tau on both sides of EC and hippocampus and increased the number of glial fibrillary acidic protein (GFAP)-positive astrocytes in the ipsilateral EC, which were prevented by the concurrent injection of Abeta1-40. These results indicate that Abeta1-40 protects neurons from Abeta1-42-induced neuronal damage in vitro and in vivo, not by sequestrating metals, but by inhibiting the beta-sheet transformation and fibril formation of Abeta1-42. Our data suggest a mechanism by which elevated Abeta1-42/Abeta1-40 ratio accelerates the development of Alzheimer's disease (AD) in familial AD.     

beta-Amyloid peptide vaccination results in marked changes in serum and brain Abeta levels in APPswe/PS1DeltaE9 mice, as detected by SELDI-TOF-based ProteinChip technology.

Although the pathogenesis of Alzheimer's disease (AD) is not fully understood, growing evidence indicates that the deposition of beta-amyloid (Abeta) and the local reactions of various cell types to this protein play major roles in the development of the disease. Immunization with the Abeta 1-42 peptide has been reported to decrease Abeta deposits in the brains of mutant amyloid precursor protein (APP/V717F) transgenic (tg) mice (Schenk et al. Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse. Nature 1999;400:173-177). We have replicated this finding in APPswe/PS1DeltaE9 tg mice, which also develop Abeta deposits in the brain. The immunized animals developed high titers of antibodies against Abeta 1-42 in serum, and Abeta deposits in the brains were significantly reduced. Using surface-enhanced laser desorption/ionization (SELDI) mass spectrometry and ProteinChip((R)) technology, we detected trends toward increased soluble Abeta peptide in the brain and a decrease in assayable Abeta peptide in the serum of immunized compared with control animals. This last finding raises the possibility that anti-Abeta antibodies in the periphery sequester Abeta peptides or target them for degradation and in this way contribute to the enhanced Abeta clearance from the brain in immunized animals.