Effect of age on the duration and extent of amyloid plaque reduction and microglial activation after injection of anti-Abeta antibody into the third ventricle of TgCRND8 mice

We have previously shown that anti beta-amyloid (Abeta) antibody injected into the third ventricle of mice is distributed throughout the brain within 24 hr and is completely washed out of brain within 36 hr after injection and that, in Tg2576 animals, a single injection of antibody reduces cerebral Abeta and restores presynaptic deficits 1 month after injection without producing hemorrhage or inflammation at an early plaque stage. Here we report the effects of a single ICV injection of anti-Abeta antibody on cerebral levels of immunoreactive Abeta and of microglial activation measured by immunoreactive interleukin-1beta (IL-1beta) at 1, 4, and 8 weeks after injections in TgCRND8 mice at two ages, 2 months (sparse plaques) and 8 months (abundant plaques). The data show that parenchymal amyloid accumulates before cerebral microvascular amyloid and that a single ICV injection reduces only parenchymal amyloid by about 70%, without affecting vascular amyloid, and reduces microglial activation by 46-60% at 1 week after injection. The reappearance of plaques after antibody injection takes 4-8 weeks, whereas plaque-associated focal microglial activation begins increasing between 1 and 4 weeks, suggesting that accumulation of nonfibrillar oligomeric Abeta may account for the earlier onset of microglial activation. No perivascular hemorrhage or inflammation was observed. These results suggest that periodic intraventricular administration of anti-Abeta is a potentially useful method for rapid reduction of both preexisting amyloid load and associated inflammation, providing a window of 4 weeks' duration for possible pharmacological cotreatment(s) to prevent de novo Abeta formation. This ICV method of passive immunization may be safer than active immunization, which has been known to produce encephalitis, or systemic passive immunization, which exposes amyloid-laden cerebral microvasculature to high levels of antibody in the blood and the potential of perivascular hemorrhages.     

Intracerebroventricular passive immunization with anti-Abeta antibody in Tg2576

Current Alzheimer's disease (AD) research has established the fact that excessive genesis of Abeta derived from amyloidogenic processing of beta-amyloid (Abeta) precursor protein is fundamental to AD pathogenesis. There has been considerable interest in using immunization strategies for clearing excessive Abeta. Studies in animal models of AD have shown that active immunizations or systemic passive immunizations reduced cerebral plaque load and improved behavioral deficits. However, clinical translation of an active immunization strategy was interrupted because of evidence for meningoencephalitis produced in some patients who received Abeta vaccine. Studies in animal models have shown perimicrovascular hemorrhages and inflammation after sustained systemic immunizations in animals with vascular amyloid. In this light, our data showing the effects of a single intracerebroventricular (ICV) injection of anti-Abeta in the Alzheimer's Swedish mutant model Tg2576 are intriguing. We have previously demonstrated that a single ICV injection of anti-Abeta into the third ventricle of 10-month-old Tg2576 mice reduced cerebral plaques, reversed Abeta-induced depletion of presynaptic SNAP-25, and abolished astroglial activation as seen 1 month post-injection (Chauhan and Siegel [2002] J. Neurosci. Res. 69:10-23). The present report demonstrates that a single ICV injection of 10 microg anti-Abeta in 10-month-old Tg2576 mice reduced cerebral plaques, with decreased inflammation at this stage as evidenced by a reduced number of interleukin-1beta-positive microglia surrounding Congophilic plaques. Moreover, at this particular age, no microhemorrhage was discernible, as evidenced by the absence of hemosiderin deposition after a single ICV injection of anti-Abeta. This is the first report demonstrating absence of microhemorrhage and reduced inflammation after the ICV introduction of anti-Abeta in Tg2576 mice at 10 months of age. These facts indicate that, although invasive, ICV injection of anti-Abeta may be a safer method of vaccination in AD, possibly through reducing the vascular exposure to antibody. Further studies are warranted to determine the lasting effects of a single ICV anti-Abeta injection in animals with and without abundant plaque burden and at older ages.     

Inter-individual variability in the expression of the mutated form of hPS1M146L determined the production of Abeta peptides in the PS1xAPP transgenic mice

The detection of the early phenotypic modifications of Alzheimer's disease (AD) models is fundamental to understand the progression and identify pharmacologic targets of this pathology. However, a large variability within different models and between age-matched mice from the same model has been observed. This variability could be due to heterogeneity in the Abeta production. Present results showed the existence of a large variability in the Abeta deposition in both hippocampus and cortex in 6-month-old PS1xAPP mice. This variability was not due to the expression of hAPP751SL, however, linear relationship between hPS1M146L mRNA and Abeta production was identified. The Abeta content was related to the incorporation of the hPS1M146L into functional gamma-secretase complexes, detected by the presence of the corresponding human or endogenous PS1-CTFs. Animals expressing low amount of hPS1M146L mRNA, displayed low hPS1-CTF incorporation and produced a low amount of Abeta peptides. Conversely, mice with relatively high hPS1 mRNA expression displayed high hPS1-CTF and high Abeta deposition. Furthermore, the Abeta total and Abeta1-42 content was increased dramatically by the expression of hPS1M146L (as compared with transgenic APPsl littermates). Therefore, variations in the expression of transgenic form of hPS1M146L in this model, or even between different models, influenced strongly the incorporation of the mutated PS1 into functional gamma-secretase complexes, the production of Abeta peptides and, in consequence, the detrimental effects of Abeta peptides. These data might implicate an "apparent gain-of-function" of the gamma-secretase complex by the expression of the mutated PS1M146L.     

Reversal of amyloid beta toxicity in Alzheimer's disease model Tg2576 by intraventricular antiamyloid beta antibody

There are considerable data on synaptic dysfunction in Alzheimer's disease (AD). However, the precise molecular basis for synaptotoxicity in AD is not known. We tested the hypothesis that amyloid beta (Abeta), as produced in Tg2576 mice overexpressing a mutant form of amyloid precursor protein, leads to changes in SNAP-25, a molecule required for Ca-sensitive neurotransmitter vesicle exocytosis. Anti-Abeta antibody was injected into the third ventricle (icv) of 10-month-old Tg2576 mice, preceding formation of plaques. Immunodensity of glial fibrillary acidic protein (GFAP) and SNAP-25 were quantitated in the hippocampus 1 month later. SNAP-25 was reduced by 96% in the inner molecular layer (SMi) of dentate gyrus, by 95% in the hilum, and by 75-76% in stratum lucidum (SL), stratum oriens (SO), and stratum radiatum (SR) of CA1-CA3 of the Tg2576 mice. GFAP was increased by more than 50-fold, specifically within the neuropil of CA1-CA3, and by twofold in portions of fimbria. One injection of 10 microg of anti-Abeta antibody into the third ventricle at 10 months completely prevented or restored changes in GFAP at 11 months of age. The restoration of SNAP-25 by anti-Abeta antibody compared with wild type was 69% in CA1-SO, 93% in CA1-SR, 85% in CA3-SL, 77% in SMi, and 60-73% in hilum. In addition, whereas control injections of saline or IgG produced greatly increased GFAP diffusely in the hippocampus of Tg2576 animals, there was no increase in GFAP after anti-Abeta injection, suggesting a synergistic interaction of nonspecific trauma with Abeta in the transgenic mice. This is the first report of depleted SNAP-25 immunoreactivity in Tg models and the first report of icv injection of anti-Abeta antibody in this model of AD. The largest reductions of the SNAP-25 are in hilum and SMi, so either reduction in the septal-hilum-SMi path is primary or reduction in this path begins at an earlier age than in CA3-CA1 fields. A single icv injection of anti-Abeta antibody is potent in reversing Abeta effects and, therefore, represents a suitable model for investigating early Abeta toxicity. In addition, intrathecal or icv antibody may be an efficient means of treating or preventing toxicity in AD, particularly under conditions of immune hyporesponsivity.     

Peripheral treatment with enoxaparin exacerbates amyloid plaque pathology in Tg2576 mice

Alzheimer's disease (AD) is a complex, progressive neurological disorder characterized by the formation of extracellular amyloid plaques composed of β‐amyloid protein (Aβ), the key component in pathogenesis of AD. Peripheral administration of enoxaparin (ENO) reportedly reduces the level of Aβ and the amyloid plaques in the cortex of amyloid precursor protein (APP) transgenic mice. However, the exact mechanism of these effects is unclear. Our previous studies indicated that ENO can inhibit APP processing to Aβ in primary cortical cells from Tg2576 mice by downregulating BACE1 levels. This study examines whether ENO‐induced reduction of amyloid load is due to the decreased APP processing to Aβ in Tg2576 mice. Surprisingly, our results indicated that ENO significantly increases the Aβ42/Aβ40 ratio in cortex and enhances the amyloid plaque load in both cortex and hippocampus, although overall APP processing was not influenced by ENO. Moreover, ENO stimulated the aggregation of both Aβ40 and Aβ42 in vitro. Although ENO has been reported to improve cognition in vivo and has potential as a therapeutic agent for AD, the results from our study suggest that ENO can exacerbate the amyloid pathology, and the strategy of using ENO for the treatment of AD may require further assessment. © 2016 Wiley Periodicals, Inc.     

Distinct presenilin-dependent and presenilin-independent gamma-secretases are responsible for total cellular Abeta production

gamma-Secretase is the second of two proteolytic enzymes involved in the liberation of the beta-amyloid peptide (Abeta) from the amyloid precursor protein (APP). gamma-Secretase cleavage occurs at several intracellular sites, including the Golgi network and the endoplasmic reticulum/intermediate compartment (ER/IC) to produce multiple forms of the Abeta peptide that can be either secreted from the cell or remain intracellular. To date, most evidence has suggested that members of the presenilin protein family are required for gamma-secretase activity. Although it seems that presenilins are indeed necessary for the production of most secreted and intracellular Abeta particularly that generated in downstream organelles, it was shown recently that a presenilin-independent gamma-secretase is active in the ER/IC and is responsible for the production of a portion of intracellular Abeta42. We discuss the implications of this finding for the understanding of presenilin biology and speculate on the putative identity of the presenilin-independent cleavage activity.     

Effect of valine on the efficiency and precision at S4 cleavage of the Notch-1 transmembrane domain

Presenilin-dependent intramembranous proteolysis mediates the dual cleavage of the Notch-1 protein (S4 and S3) as well as the beta amyloid precursor protein (betaAPP) (gamma40 and epsilon-site). betaAPP has a valine residue just before the gamma40 (amyloid beta [Abeta] numbering) site and after the epsilon-site. Both gamma40 and epsilon have multiple cleavage sites, and the varieties of gamma40 cleavage are associated with Alzheimer's disease (AD). These lines of evidence suggest that valine plays a role in the intramembranous proteolysis. S4 cleavage in the middle of the Notch-1 transmembrane domain (TMD) corresponds to the gamma40 cleavage of betaAPP. The cleavage site is in the center of four sequential alanine residues between Ala1731 and Ala1732, neither of which has a valine residue. To investigate the effects of valine on presenilin-dependent intramembranous proteolysis, we replaced the transmembrane domain residue of Notch-1 with valine and analyzed the efficiency and precision at S4 and S3. We observed that all valine-mutated Notch-1 proteins have a dominant cleavage site (S4) between Ala1731 and Ala1732 with some variations of cleavage precision, suggesting that valine is not indispensable for determining the cleavage site of the Notch-1 transmembrane domain, but affects the efficiency and precision at S4 cleavage of the Notch-1 transmembrane domain.     

Tauopathy with paired helical filaments in an aged chimpanzee

An enigmatic feature of age-related neurodegenerative diseases is that they seldom, if ever, are fully manifested in nonhuman species under natural conditions. The neurodegenerative tauopathies are typified by the intracellular aggregation of hyperphosphorylated microtubule-associated protein tau (MAPT) and the dysfunction and death of affected neurons. We document the first case of tauopathy with paired helical filaments in an aged chimpanzee (Pan troglodytes). Pathologic forms of tau in neuronal somata, neuropil threads, and plaque-like clusters of neurites were histologically identified throughout the neocortex and, to a lesser degree, in allocortical and subcortical structures. Ultrastructurally, the neurofibrillary tangles consisted of tau-immunoreactive paired helical filaments with a diameter and helical periodicity indistinguishable from those seen in Alzheimer's disease. A moderate degree of Abeta deposition was present in the cerebral vasculature and, less frequently, in senile plaques. Sequencing of the exons and flanking intronic regions in the genomic MAPT locus disclosed no mutations that are associated with the known human hereditary tauopathies, nor any polymorphisms of obvious functional significance. Although the lesion profile in this chimpanzee differed somewhat from that in Alzheimer's disease, the copresence of paired helical filaments and Abeta-amyloidosis indicates that the molecular mechanisms for the pathogenesis of the two canonical Alzheimer lesions--neurofibrillary tangles and senile plaques--are present in aged chimpanzees.     

Transforming growth factor beta2 autocrinally mediates neuronal cell death induced by amyloid-beta

Amyloid beta (Abeta), the major component of the senile plaques of Alzheimer's disease, is implicated in neuronal cell death. We have found that Abeta42, a neurotoxic form of Abeta peptide, induces both neuronal and glial expression of TGFbeta2. We have further demonstrated that the addition into culture media of neutralizing antibody to TGFbeta2 or a large amount of the recombinant soluble amyloid precursor protein alpha, the extracellular domain of amyloid precursor protein (APP) generated by alpha secretase, suppresses death in primary cortical neurons (PCNs) induced by Abeta42 in vitro. Combined with the finding in our recent study indicating that TGFbeta2 is a neuronal cell death-inducing ligand for APP, it is suggested that TGFbeta2 is an autocrinal mediator for Abeta42-induced death in PCNs.     

Age- and concentration-dependent neuroprotection and toxicity by TNF in cortical neurons from beta-amyloid

The induction of an inflammatory response and release of cytokines such as TNF may be involved in the age-related etiology of Alzheimer disease (AD). In the brain, microglia have been shown to produce a wide variety of immune mediators, including the pro-inflammatory cytokine tumor necrosis factor (TNF). We hypothesize that with age there is increased ability of microglia to produce TNF or that age decreases the neuroprotective effect of TNF against beta-amyloid (Abeta) toxicity in neurons. We investigated the effects of Abeta(1-40) on TNF secretion from forebrain cultures of microglia from embryonic, middle-age (9-month) and old (36-month) rats. Over the first 12 hr of exposure to 10 microM Abeta (1-40), microglia from embryonic and old rats increase TNF secretion, although microglia from middle-age rats did not produce detectable levels of TNF. When low concentrations of TNF are added to neurons together with Abeta (1-40) in the absence of exogenous antioxidants, neuroprotection for old neurons is significantly less than neuroprotection for middle-age neurons. In neurons from old rats, high levels of TNF together with Abeta are more toxic than in neurons from middle-age or embryonic rats. These results are discussed in relation to neuroprotection and toxicity of the age-related pathology of AD.     

Residues 17-20 and 30-35 of beta-amyloid play critical roles in aggregation

We examined the effects of co-incubating nine different Abeta peptide fragments with full-length Abeta1-40 (Abeta40) on protein aggregation. Six fragments enhanced aggregation of Abeta40 (Abeta1-28, 12-28, 17-28, 10-20, 25-35 and 17-40), while three others did not (Abeta1-11, 1-16, and 20-29). All of the peptides that enhanced aggregation contained either residues 17-20 or 30-35, indicating the importance of these regions for promoting aggregation of full-length Abeta. Abeta25-35 in particular increased both the rate and extent of aggregation of Abeta40 considerably as indicated by fluorescence staining. Atomic force microscope imaging (AFM) indicates the increase in fluorescence staining with Abeta25-35 is primarily due to increased formation of oligomers and protofibrils rather than formation of large amyloid fibrils. AFM images of Abeta25-35 when incubated alone also indicate formation of aggregates and long thin filaments. The increase in formation of the small toxic oligomeric morphology of Abeta40, along with formation of Abeta25-35 oligomers and thin filaments, represent two different potential pathways for Abeta25-35 toxicity. The critical roles of residues 17-20 and 30-35 of Abeta provide further insight into mechanism that underlie the formation of toxic aggregates in Alzheimer Disease (AD) and suggest targets for the design of beta-sheet breakers to modulate the aggregation and inhibit toxicity of full-length Abeta.     

Cerebral vascular accumulation of Dutch-type Abeta42, but not wild-type Abeta42, in hereditary cerebral hemorrhage with amyloidosis, Dutch type

Hereditary cerebral hemorrhage with amyloidosis, Dutch type (HCHWA-D), is an autosomal dominant disorder caused by the Dutch mutation (E693Q) in the beta-amyloid precursor protein. This mutation produces an aberrant amyloid beta (Abeta) species (AbetaE22Q) and causes severe meningocortical vascular Abeta deposition. We analyzed the Abeta composition of the vascular amyloid in the brains of HCHWA-D patients. Immunohistochemistry demonstrated that the vascular amyloid contained both Abeta40 and Abeta42, with a high Abeta40/Abeta42 ratio. In Western blotting of cerebral microvessel fractions isolated from the brains, both wild-type and Dutch-type Abeta40 were observed as major species. Reverse-phase HPLC-mass spectrometric analysis of the fractions revealed both wild-type and Dutch-type Abeta38 as the other main components of the vascular amyloid. Moreover, we detected peaks corresponding to Dutch-type Abeta42 but not to wild-type Abeta42. These results suggest a pathogenic role for the mutant Abeta42 in addition to the mutant Abeta40 in the cerebral amyloid angiopathy of HCHWA-D.     

Limited expression of heparan sulphate proteoglycans associated with Aβ deposits in the APPswe/PS1dE9 mouse model for Alzheimer's disease

N. M. Timmer, M. K. Herbert, J. W. Kleinovink, A. J. Kiliaan, R. M. W. de Waal and M. M. Verbeek (2010) Neuropathology and Applied Neurobiology 36, 478–486
Limited expression of heparan sulphate proteoglycans associated with Aβ deposits in the APPswe/PS1dE9 mouse model for Alzheimer's disease Aims: Alzheimer's disease (AD) is characterized by deposition of the amyloid beta (Aβ) peptide in brain parenchyma and vasculature. Several proteins co‐deposit with Aβ, including heparan sulphate proteoglycans (HSPG). HSPG have been suggested to contribute to Aβ aggregation and deposition, and may influence plaque formation and persistence by stimulating Aβ fibrillization and by protecting Aβ against degradation. Mouse models for AD, expressing the human amyloid precursor protein (APP), produce Aβ deposits similar to humans. These models may be used to study disease pathology and to develop new therapeutic interventions. We aimed to investigate whether co‐deposition of HSPG in AD brains can be replicated in the APPswe/PS1dE9 mouse model for AD and if a temporal association of HSPG with Aβ exists. Methods: We studied the co‐deposition of several HSPG and of the glycosaminoglycan side chains of HSPG in the APPswe/PS1dE9 model at different ages by immunohistochemistry. Results: We found that, although APPswe/PS1dE9 mice did develop severe Aβ pathology with age, co‐deposition of HS glycosaminoglycan chains and the various HSPG (agrin, perlecan and glypican‐1) was scarce (<10–30% of the Aβ deposits were stained). Conclusions: Our data suggest that the molecular composition of Aβ deposits in the APPswe/PS1dE9 mouse, with respect to the several HSPG investigated in this study, does not accurately reflect the human situation. The near absence of HSPG in Aβ deposits in this transgenic mouse model may, in turn, hinder the translation of preclinical intervention studies from mice to men.     

Beta-amyloid (25-35) enhances lipid metabolism and protein ubiquitination in cultured neurons

We investigated the effect of beta-amyloid (Abeta) (25-35), a cytotoxic fragment of Abeta peptide, on lipid metabolism and protein ubiquitination in cultured rat hippocampal neurons. After treatment with Abeta under conditions leading to apoptotis, as assessed by caspase activity assay, the total cell mass of lipids changed following a biphasic behavior, with an increase that reached a maximum after 16 hr of treatment, followed by a decrease. The increase at 16 hr was 15.3% in the case of phospholipids and 103.0% in the case of gangliosides and was due to enhanced biosynthesis as confirmed by increase of radioactivity incorporation (phospholipids +52.0%, gangliosides +193.1%) in cells fed with tritiated palmitic acid. No change with respect to cholesterol was observed. Strikingly, under these conditions, the ubiquitination state of cell proteins strongly increased. These effects were not observed with the (35-25) reverse sequence peptide. Similarly to Abeta, lactacystin treatment increased lipid synthesis and protein ubiquitination; only lactacystin, and not Abeta, induced a strong decrease of proteasome chimotrypsin activity. These results suggest that Abeta enhances protein ubiquitination, without inhibiting proteasomal activity, and lipid synthesis. These results may shed new light on the mechanisms of Abeta toxicity.     

Cysteine proteases are the major beta-secretase in the regulated secretory pathway that provides most of the beta-amyloid in Alzheimer's disease: role of BACE 1 in the constitutive secretory pathway

This article focuses on beta-amyloid (Abeta) peptide production and secretion in the regulated secretory pathway and how this process relates to accumulation of toxic Abeta in Alzheimer's disease. New findings are presented demonstrating that most of the Abeta is produced and secreted, in an activity-dependent manner, through the regulated secretory pathway in neurons. Only a minor portion of cellular Abeta is secreted via the basal, constitutive secretory pathway. Therefore, regulated secretory vesicles contain the primary beta-secretases that are responsible for producing the majority of secreted Abeta. Investigation of beta-secretase activity in regulated secretory vesicles of neuronal chromaffin cells demonstrated that cysteine proteases account for the majority of the beta-secretase activity. BACE 1 is present in regulated secretory vesicles but provides only a small percentage of the beta-secretase activity. Moreover, the cysteine protease activities prefer to cleave the wild-type beta-secretase site, which is relevant to the majority of AD cases. In contrast, BACE 1 prefers to cleave the Swedish mutant beta-secretase site that is expressed in a minor percentage of the AD population. These new findings lead to a unifying hypothesis in which cysteine proteases are the major beta-secretases for the production of Abeta in the major regulated secretory pathway and BACE 1 is the beta-secretase responsible for Abeta production in the minor constitutive secretory pathway. These results indicate that inhibition of multiple proteases may be needed to decrease Abeta production as a therapeutic strategy for Alzheimer's disease.     

Dissociation of β-amyloid from lipoprotein in cerebrospinal fluid from Alzheimer's disease accelerates β-amyloid-42 assembly

Monoclonal 2C3 specific to β-amyloid (Aβ) oligomers (AβOs) enabled us to test our hypothesis that the alteration of lipoprotein-Aβ interaction in the central nervous system (CNS) initiates and/or accelerates the cascade favoring Aβ assembly. Immunoprecipitation of frontal cortex employing 2C3 unequivocally detected soluble 4-, 8-, and 12-mers in Alzheimer's disease (AD) brains. Immunoblot analysis of the entorhinal cortex employing 2C3 revealed that the accumulation of soluble 12-mers precedes the appearance of neuronal loss or cognitive impairment and is enhanced as the Braak neurofibrially tangle (NFT) stages progress. The dissociation of soluble Aβ from lipoprotein particles occurs in cerebrospinal fluid (CSF), and the presence of lipoprotein-free oligomeric 2C3 conformers (4- to 35-mers) was evident, which mimic CNS environments. Such CNS environments may strongly affect conformation of soluble Aβ peptides, resulting in the conversion of soluble Aβ(42) monomers into soluble Aβ(42) assembly. The findings suggest that functionally declined lipoproteins may accelerate the generation of metabolic conditions leading to higher levels of soluble Aβ(42) assembly in the CNS.     

Depression is associated with low plasma Abeta42 independently of cardiovascular disease in the homebound elderly

BACKGROUND: Depression often precedes the onset of Alzheimer's disease (AD) before the appearance of cognitive symptoms. Plasma Amyloid-beta peptide 42 (Abeta42) declines before and soon after the onset of AD, yet the relationship between plasma Abeta42 and depression is unclear. METHODS: We used 515 homebound elders aged 60 and older in a population-based, cross-sectional study to investigate associations between plasma Abeta levels and depression with and without cardiovascular co-morbidities. Depression was evaluated by using the Center for Epidemiological Studies Depression (CES-D) scale. Plasma Abeta40 and Abeta42 were measured. RESULTS: The elderly with depression had lower plasma Abeta42 (median: 15.3 vs. 18.9, p = 0.008) than those without depression. The CES-D score was inversely associated with plasma Abeta42 (p = 0.001) in subjects with no cardiovascular disease (CVD); however, in the presence of CVD, this association did not exist. Low plasma Abeta42 (OR = 0.41, p = 0.007) and the presence of CVD (OR = 1.84, p = 0.005) were independently associated with depression after adjusting for the confounders of age, stroke and apolipoprotein E4. CONCLUSIONS: Depressive symptoms are associated with low plasma Abeta42 independently of CVD. Prospective studies are needed to determine whether depression associated with low plasma Abeta42 is a separate depression subtype that could predict the onset of AD.     

An amyloid-β protofibril-selective antibody prevents amyloid formation in a mouse model of Alzheimer's disease

Human genetics link Alzheimer's disease pathogenesis to excessive accumulation of amyloid-β (Aβ) in brain, but the symptoms do not correlate with senile plaque burden. Since soluble Aβ aggregates can cause synaptic dysfunctions and memory deficits, these species could contribute to neuronal dysfunction and dementia. Here we explored selective targeting of large soluble aggregates, Aβ protofibrils, as a new immunotherapeutic strategy. The highly protofibril-selective monoclonal antibody mAb158 inhibited in vitro fibril formation and protected cells from Aβ protofibril-induced toxicity. When the mAb158 antibody was administered for 4 months to plaque-bearing transgenic mice with both the Arctic and Swedish mutations (tg-ArcSwe), Aβ protofibril levels were lowered while measures of insoluble Aβ were unaffected. In contrast, when treatment began before the appearance of senile plaques, amyloid deposition was prevented and Aβ protofibril levels diminished. Therapeutic intervention with mAb158 was however not proven functionally beneficial, since place learning depended neither on treatment nor transgenicity. Our findings suggest that Aβ protofibrils can be selectively cleared with immunotherapy in an animal model that display highly insoluble Aβ deposits, similar to those of Alzheimer's disease brain.     

Distribution of intraventricularly administered antiamyloid-beta peptide (Abeta) antibody in the mouse brain

There is considerable interest in utilizing the intracerebroventricular (icv) route of administration of antibodies in the brain for various studies and for the therapy of malignancies, but very little is known about the anatomic extent of distribution of the antibody in brain after injection into the third ventricle. To explore the potential for icv administration of antiamyloid-beta peptide (Abeta) in reducing Abeta toxicity in brain in Alzheimer's disease, we first mapped the time course and path of transit of horseradish peroxidase (HRP)-labeled antibody. The results show that, after a single injection into the mouse third venticle, the HRP-labeled antibody is localized within the microvasculature, first that of the corticohippocampal region close to the site of injection at 3 hr. By 24 hr, the antibody is distributed throughout the hippocampus and frontoparietal cortex close to the injection site, as well as in the deep and outer cerebral cortex and cerebellar cortex remote from the injection site. The injected antibody is almost entirely removed by 4 days. Therefore, the antibody had diffused throughout all the brain by 24 hr, showing the feasibility of small quantities of anti-Abeta antibody infused into the third ventricle to reach extracellular epitopes throughout the brain parenchyma rapidly.