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Alzheimer's disease (AD) is associated with accumulation of beta-amyloid (Abeta). A major genetic risk factor for sporadic AD is inheritance of the apolipoprotein (apo) E4 allele. ApoE can act as a pathological chaperone of Abeta, promoting its conformational transformation from soluble Abeta into toxic aggregates. We determined if blocking the apoE/Abeta interaction reduces Abeta load in transgenic (Tg) AD mice. The binding site of apoE on Abeta corresponds to residues 12 to 28. To block binding, we synthesized a peptide containing these residues, but substituted valine at position 18 to proline (Abeta12-28P). This changed the peptide's properties, making it non-fibrillogenic and non-toxic. Abeta12-28P competitively blocks binding of full-length Abeta to apoE (IC50 = 36.7 nmol). Furthermore, Abeta12-28P reduces Abeta fibrillogenesis in the presence of apoE, and Abeta/apoE toxicity in cell culture. Abeta12-28P is blood-brain barrier-permeable and in AD Tg mice inhibits Abeta deposition. Tg mice treated with Abeta12-28P for 1 month had a 63.3% reduction in Abeta load in the cortex (P = 0.0043) and a 59.5% (P = 0.0087) reduction in the hippocampus comparing to age-matched control Tg mice. Antibodies against Abeta were not detected in sera of treated mice; therefore the observed therapeutic effect of Abeta12-28P cannot be attributed to an antibody clearance response. Our experiments demonstrate that compounds blocking the interaction between Abeta and its pathological chaperones may be beneficial for treatment of beta-amyloid deposition in AD.

The amyloid-␤ (A␤) cascade hypothesis of Alzheimer's disease (AD) maintains that accumulation of A␤ peptide constitutes a critical event in the early disease pathogenesis. The direct binding between A␤ and apolipoprotein E (apoE) is an important factor implicated in both A␤ clearance and its deposition in the brain's parenchyma and the walls of meningoencephalic vessels as cerebral amyloid angiopathy. With the aim of testing the effect of blocking the apoE/A␤ interaction in vivo as a potential novel therapeutic target for AD pharmacotherapy, we have developed A␤12-28P, which is a blood-brain-barrier-permeable nontoxic, and nonfibrillogenic synthetic peptide homologous to the apoE binding site on the full-length A␤. A␤12-28P binds with high affinity to apoE, preventing its binding to A␤, but has no direct effect on A␤ aggregation. A␤12-28P shows a strong pharmacological effect in vivo. Its systemic administration resulted in a significant reduction of A␤ plaques and cerebral amyloid angiopathy burden and a reduction of the total brain level of A␤ in two AD transgenic mice models. The treatment did not affect the levels of soluble A␤ fraction or A␤ oligomers, indicating that inhibition of the apoE/A␤ interaction in vivo has a net effect of increasing A␤ clearance over deposition and at the same time does not create conditions favoring formation of toxic oligomers. Furthermore, behavioral studies demonstrated that treatment with A␤12-28P prevents a memory deficit in transgenic animals. These findings provide evidence of another therapeutic approach for AD.Alzheimer's pathology ͉ memory loss prevention ͉ peptide ͉ transgenic mice ͉ treatment A lzheimer's disease (AD) is the most common neurodegenerative disease worldwide, characterized by a progressive dysfunction in multiple cognitive domains and complex neuropathological features that include accumulation of amyloid-␤ (A␤) followed by synaptic dysfunction, formation of neurofibrillary tangles, and neuronal loss. With the expected increase in AD prevalence, as a function of the population aging, effective treatment for AD is critically needed. Multiple lines of evidence indicate that a disturbance of A␤ homeostasis is a paramount event in early disease pathogenesis (1). A␤ is a hydrophobic 39-to 43-aa peptide, which is derived from cleavage of a larger, synaptic transmembrane protein, the amyloid precursor protein (APP) (2). The accumulation of A␤ in the brain is determined by the rate of its generation versus in situ proteolytic degradation and clearance across the blood-brain-barrier [BBB; for review see Tanzi et al. (3)]. In the setting of increased concentration, A␤ monomers assemble into oligomers and fibrils and eventually become deposited, forming parenchymal plaques and cerebral amyloid angiopathy (CAA).Inheritance of the apolipoprotein E4 (apoE4) allele is the strongest genetic risk factor identified so far. ApoE isotype inheritance modulates the prevalence, age of onset, and the burden of pathology in sporadic AD (4, 5). ApoE binds A␤ with high affinity a...

Prion diseases are transmissible and invariably fatal neurodegenerative disorders associated with a conformational transformation of the cellular prion protein (PrP C ) into a self-replicating and proteinase K (PK)-resistant conformer, scrapie PrP (PrP Sc ). Humoral immunity may significantly prolong the incubation period and even prevent disease in murine models of prionoses. However, the mechanism(s) of action of anti-PrP monoclonal antibodies (Mabs) remain(s) obscure. The murine neuroblastoma N2a cell line, infected with the 22L mouse-adapted scrapie strain, was used to screen a large library of Mabs with similar binding affinities to PrP, to identify those antibodies which could clear established infection and/or prevent infection de novo. Three Mabs were found capable of complete and persistent clearing of already-infected N2a cells of PrP Sc . These antibodies were 6D11 (generated to PK-resistant PrP Sc and detecting PrP residues 93-109), and 7H6 and 7A12, which were raised against recombinant PrP and react with neighbouring epitopes of PrP residues 130-140 and 143-155, respectively. Mabs were found to interact with PrP Sc formation both on the cell surface and after internalization in the cytosol. Treatment with Mabs was not associated with toxicity nor did it result in decreased expression of PrP C . Both preincubation of N2a cells with Mabs prior to exposure to 22L inoculum and preincubation of the inoculum with Mabs prior to infecting N2a cells resulted in a significant reduction in PrP Sc levels. Information provided in these studies is important for the rational design of humoral immune therapy for prion infection in animals and eventually in humans.

No abstract

Accumulation of β-amyloid (Aβ) in the brain is a key event in Alzheimer disease pathogenesis. Apolipoprotein (Apo) E is a lipid carrier protein secreted by astrocytes, which shows inherent affinity for Aβ and has been implicated in the receptor-mediated Aβ uptake by neurons. To characterize ApoE involvement in the intraneuronal Aβ accumulation and to investigate whether blocking the ApoE/Aβ interaction could reduce intraneuronal Aβ buildup, we used a noncontact neuronal-astrocytic co-culture system, where synthetic Aβ peptides were added into the media without or with cotreatment with Aβ12-28P, which is a nontoxic peptide antagonist of ApoE/Aβ binding. Compared with neurons cultured alone, intraneuronal Aβ content was significantly increased in neurons co-cultured with wild-type but not with ApoE knockout (KO) astrocytes. Neurons co-cultured with astrocytes also showed impaired intraneuronal degradation of Aβ, increased level of intraneuronal Aβ oligomers, and marked down-regulation of several synaptic proteins. Aβ12-28P treatment significantly reduced intraneuronal Aβ accumulation, including Aβ oligomer level, and inhibited loss of synaptic proteins. Furthermore, we showed significantly reduced intraneuronal Aβ accumulation in APPSW/PS1dE9/ApoE KO mice compared with APPSW/PS1dE9/ApoE targeted replacement mice that expressed various human ApoE isoforms. Data from our co-culture and in vivo experiments indicate an essential role of ApoE in the mechanism of intraneuronal Aβ accumulation and provide evidence that ApoE/Aβ binding antagonists can effectively prevent this process.

The major neuropathological lesions defining Alzheimer's disease (AD) include neurofibrillary tangles and amyloid plaques, which are mainly composed of abnormally phosphorylated tau and amyloid-beta (A beta), respectively. Numerous neuropathological and neuroimaging studies indicate that at least one-third of AD cases are complicated by some degree of vascular pathology, whereas in a similar proportion of patients clinically diagnosed with vascular dementia, AD pathology is also present. Many classical vascular risk factors such as hypertension, diabetes mellitus, and hypercholesterolemia have recently been shown also to increase the risk of AD. Growing evidence suggests that vascular pathology lowers the threshold for the clinical presentation of dementia at a given level of AD-related pathology and potentially directly promotes AD lesions such as A beta plaques. Cerebral ischemia, chronically up-regulates expression of the amyloid precursor protein (APP), which is the precursor to the amyloid beta peptide and damages the blood-brain barrier (BBB), affecting A beta peptide clearance from the brain. Recognition of the importance of these vascular risk factors for AD-related dementia and their treatment will be beneficial not only for preventing cardiac, cerebral, and peripheral complications of vascular disease, but also will likely have a direct impact on the occurrence of sporadic AD in older subjects. In this paper, we review some of the links between vascular risk factors and AD pathology and present data on the direct effect of ischemia on cognitive function and A beta deposition in a mouse model of AD.

The pathogenesis of prion diseases is related to conformational transformation of cellular prion protein (PrP C ) into a toxic, infectious, and self-replicating conformer termed PrP Sc . Following extracerebral inoculation, the replication of PrP Sc is confined for months to years to the lymporeticular system (LRS) before the secondary CNS involvement results in occurrence of neurological symptoms. Therefore, replication of PrP Sc , in the early stage of infection can be targeted by therapeutic approaches, which like passive immunization have limited blood-brain-barrier penetration. In this study, we show that 6D11 anti-PrP monoclonal antibody (Mab) prevents infection on a FDC-P1 myeloid precursor cell line stably infected with 22L mouse adapted scrapie strain. Passive immunization of extracerebrally infected CD-1 mice with Mab 6D11 resulted in effective suppression of PrP Sc replication in the LRS. Although, a rebound of PrP Sc presence occurred when the Mab 6D11 treatment was stopped, passively immunized mice showed a prolongation of the incubation period by 36.9% (p<0.0001) and a significant decrease in CNS pathology compared to control groups receiving vehicle or murine IgG. Our results indicate that antibody-based therapeutic strategies can be used, even on a short-term basis, to delay or prevent disease in subjects accidentally exposed to prions.