Anti-α-synuclein immunotherapy reduces α-synuclein propagation in the axon and degeneration in a combined viral vector and transgenic model of synucleinopathy

Neurodegenerative disorders such as Parkinson's Disease (PD), PD dementia (PDD) and Dementia with Lewy bodies (DLB) are characterized by progressive accumulation of α-synuclein (α-syn) in neurons. Recent studies have proposed that neuron-to-neuron propagation of α-syn plays a role in the pathogenesis of these disorders. We have previously shown that antibodies against the C-terminus of α-syn reduce the intra-neuronal accumulation of α-syn and related deficits in transgenic models of synucleinopathy, probably by abrogating the axonal transport and accumulation of α-syn in in vivo models. Here, we assessed the effect of passive immunization against α-syn in a new mouse model of axonal transport and accumulation of α-syn. For these purpose, non-transgenic, α-syn knock-out and mThy1-α-syn tg (line 61) mice received unilateral intra-cerebral injections with a lentiviral (LV)-α-syn vector construct followed by systemic administration of the monoclonal antibody 1H7 (recognizes amino acids 91-99) or control IgG for 3 months. Cerebral α-syn accumulation and axonopathy was assessed by immunohistochemistry and effects on behavior were assessed by Morris water maze. Unilateral LV-α-syn injection resulted in axonal propagation of α-syn in the contra-lateral site with subsequent behavioral deficits and axonal degeneration. Passive immunization with 1H7 antibody reduced the axonal accumulation of α-syn in the contra-lateral side and ameliorated the behavioral deficits. Together this study supports the notion that immunotherapy might improve the deficits in models of synucleinopathy by reducing the axonal propagation and accumulation of α-syn. This represents a potential new mode of action through which α-syn immunization might work.

Secreted amyloid β-proteins in a cell culture model include N-terminally extended peptides that impair synaptic plasticity

Evidence for a central role of amyloid β-protein (Aβ) in the genesis of Alzheimer’s disease (AD) has led to advanced human trials of Aβ-lowering agents. The “amyloid hypothesis” of AD postulates deleterious effects of small, soluble forms of Aβ on synaptic form and function. Because selectively targeting synaptotoxic forms of soluble Aβ could be therapeutically advantageous, it is important to understand the full range of soluble Aβ derivatives. We previously described a Chinese hamster ovary (CHO) cell line (7PA2 cells) that stably expresses mutant human amyloid precursor protein (APP). Here, we extend this work by purifying an sodium dodecyl sulfate (SDS)-stable, ∼8 kDa Aβ species from the 7PA2 medium. Mass spectrometry confirmed its identity as a noncovalently bonded Aβ40 homodimer that impaired hippocampal long-term potentiation (LTP) in vivo. We further report the detection of Aβ-containing fragments of APP in the 7PA2 medium that extend N-terminal from Asp1 of Aβ. These N-terminally extended Aβ-containing monomeric fragments are distinct from soluble Aβ oligomers formed from Aβ1-40/42 monomers and are bioactive synaptotoxins secreted by 7PA2 cells. Importantly, decreasing β-secretase processing of APP elevated these alternative synaptotoxic APP fragments. We conclude that certain synaptotoxic Aβ-containing species can arise from APP processing events N-terminal to the classical β-secretase cleavage site.

Axonopathy in an α-synuclein transgenic model of Lewy body disease is associated with extensive accumulation of C-terminal-truncated α-synuclein

Progressive accumulation of α-synuclein (α-syn) in limbic and striatonigral systems is associated with the neurodegenerative processes in dementia with Lewy bodies (DLB) and Parkinson's disease (PD). The murine Thy-1 (mThy1)-α-syn transgenic (tg) model recapitulates aspects of degenerative processes associated with α-syn accumulation in these disorders. Given that axonal and synaptic pathologies are important features of DLB and PD, we sought to investigate the extent and characteristics of these alterations in mThy1-α-syn tg mice and to determine the contribution of α-syn c-terminally cleaved at amino acid 122 (CT α-syn) to these abnormalities. We generated a novel polyclonal antibody (SYN105) against the c-terminally truncated sequence (amino acids 121 to 123) of α-syn (CT α-syn) and performed immunocytochemical and ultrastructural analyses in mThy1-α-syn tg mice. We found abundant clusters of dystrophic neurites in layers 2 to 3 of the neocortex, the stratum lacunosum, the dentate gyrus, and cornu ammonis 3 of the hippocampus, striatum, thalamus, midbrain, and pons. Dystrophic neurites displayed intense immunoreactivity detected with the SYN105 antibody. Double-labeling studies with antibodies to phosphorylated neurofilaments confirmed the axonal location of full-length and CT α-syn. α-Syn immunoreactive dystrophic neurites contained numerous electrodense laminated structures. These results show that neuritic dystrophy is a prominent pathologic feature of the mThy1-α-syn tg model and suggest that CT α-syn might play an important role in the process of axonal damage in these mice as well as in DLB and PD.

AL amyloid imaging and therapy with a monoclonal antibody to a cryptic epitope on amyloid fibrils

The monoclonal antibody 2A4 binds an epitope derived from a cleavage site of serum amyloid protein A (sAA) containing a -Glu-Asp- amino acid pairing. In addition to its reactivity with sAA amyloid deposits, the antibody was also found to bind amyloid fibrils composed of immunoglobulin light chains. The antibody binds to synthetic fibrils and human light chain (AL) amyloid extracts with high affinity even in the presence of soluble light chain proteins. Immunohistochemistry with biotinylated 2A4 demonstrated positive reaction with ALκ and ALλ human amyloid deposits in various organs. Surface plasmon resonance analyses using synthetic AL fibrils as a substrate revealed that 2A4 bound with a K_D of ∼10 nM. Binding was inhibited in the presence of the –Glu-Asp- containing immunogen peptide. Radiolabeled 2A4 specifically localized with human AL amyloid extracts implanted in mice (amyloidomas) as evidenced by single photon emission (SPECT) imaging. Furthermore, co-localization of the radiolabeled mAb with amyloid was shown in biodistribution and micro-autoradiography studies. Treatment with 2A4 expedited regression of ALκ amyloidomas in mice, likely mediated by the action of macrophages and neutrophils, relative to animals that received a control antibody. These data indicate that the 2A4 mAb might be of interest for potential imaging and immunotherapy in patients with AL amyloidosis.

Generation and characterization of anti-AA amyloid-specific monoclonal antibodies

AA amyloidosis results from the pathologic deposition in the kidneys and other organs of fibrils composed of N-terminal fragments of serum amyloid A protein (SAA). Given that there are only limited means to visualize these deposits, we have developed a series of mAbs, 2A4, 7D8, and 8G9, that bind specifically with nanomolar affinity to a carboxy-terminal epitope generated following proteolysis of SAA that yields the predominant component of AA amyloid deposits. Notably, these antibodies do not recognize native SAA, they retain their immunoreactivity when radiolabeled with I-125 and, after injection into AA amyloidotic mice, localize, as evidenced by autoradiography and micro-single photon emission computed tomography imaging, to histologically confirmed areas of amyloid deposition; namely, spleen, liver, and pancreas. The results of our in vitro and in vivo studies demonstrate the AA fibril-selectivity of mAbs 2A4, 7D8, and 8G9 and warrant further investigation into their role as novel diagnostic agents for patients with AA amyloidosis.

Passive immunization reduces behavioral and neuropathological deficits in an alpha-synuclein transgenic model of Lewy body disease

Dementia with Lewy bodies (DLB) and Parkinson's Disease (PD) are common causes of motor and cognitive deficits and are associated with the abnormal accumulation of alpha-synuclein (α-syn). This study investigated whether passive immunization with a novel monoclonal α-syn antibody (9E4) against the C-terminus (CT) of α-syn was able to cross into the CNS and ameliorate the deficits associated with α-syn accumulation. In this study we demonstrate that 9E4 was effective at reducing behavioral deficits in the water maze, moreover, immunization with 9E4 reduced the accumulation of calpain-cleaved α-syn in axons and synapses and the associated neurodegenerative deficits. In vivo studies demonstrated that 9E4 traffics into the CNS, binds to cells that display α-syn accumulation and promotes α-syn clearance via the lysosomal pathway. These results suggest that passive immunization with monoclonal antibodies against the CT of α-syn may be of therapeutic relevance in patients with PD and DLB.

Amyloid precursor protein (APP) processing genes and cerebrospinal fluid APP cleavage product levels in Alzheimer's disease

The aim of this exploratory investigation was to determine if genetic variation within amyloid precursor protein (APP) or its processing enzymes correlates with APP cleavage product levels: APPα, APPβ or Aβ42, in cerebrospinal fluid (CSF) of cognitively normal subjects or Alzheimer's disease (AD) patients. Cognitively normal control subjects (n = 170) and AD patients (n = 92) were genotyped for 19 putative regulatory tagging SNPs within 9 genes (APP, ADAM10, BACE1, BACE2, PSEN1, PSEN2, PEN2, NCSTN and APH1B) involved in the APP processing pathway. SNP genotypes were tested for their association with CSF APPα, APPβ, and Aβ42, AD risk and age-at-onset while taking into account age, gender, race and APOE ε4. After adjusting for multiple comparisons, a significant association was found between ADAM10 SNP rs514049 and APPα levels. In controls, the rs514049 CC genotype had higher APPα levels than the CA, AA collapsed genotype, whereas the opposite effect was seen in AD patients. These results suggest that genetic variation within ADAM10, an APP processing gene, influences CSF APPα levels in an AD specific manner.

Structural correlates of antibodies associated with acute reversal of amyloid beta-related behavioral deficits in a mouse model of Alzheimer disease

Immunotherapy targeting of amyloid beta (Abeta) peptide in transgenic mouse models of Alzheimer disease (AD) has been widely demonstrated to resolve amyloid deposition as well as associated neuronal, glial, and inflammatory pathologies. These successes have provided the basis for ongoing clinical trials of immunotherapy for treatment of AD in humans. Acute as well as chronic Abeta-targeted immunotherapy has also been demonstrated to reverse Abeta-related behavioral deficits assessing memory in AD transgenic mouse models. We observe that three antibodies targeting the same linear epitope of Abeta, Abeta(3-7), differ in their ability to reverse contextual fear deficits in Tg2576 mice in an acute testing paradigm. Reversal of contextual fear deficit by the antibodies does not correlate with in vitro recognition of Abeta in a consistent or correlative manner. To better define differences in antigen recognition at the atomic level, we determined crystal structures of Fab fragments in complex with Abeta. The conformation of the Abeta peptide recognized by all three antibodies was highly related and is also remarkably similar to that observed in independently reported Abeta:antibody crystal structures. Sequence and structural differences between the antibodies, particularly in CDR3 of the heavy chain variable region, are proposed to account for differing in vivo properties of the antibodies under study. These findings provide a structural basis for immunotherapeutic strategies targeting Abeta species postulated to underlie cognitive deficits in AD.

The role of animal models in advancing amyloid-beta immunotherapy to the clinic

The amyloid-beta (Aβ) hypothesis of Alzheimer's disease (AD) causality is now well into its third decade and is finally entering a phase of rigorous clinical testing in numerous late stage clinical trials. The use of Aβ-based animal models of AD has been essential to the discovery and/or preclinical validation of many of these therapeutic approaches. While several neuropathologically based results from preclinical studies have translated nicely into AD patients, the full clinical value of Aβ-directed therapies awaits results from trials now in progress.

Progress in the active immunotherapeutic approach to Alzheimer's disease: clinical investigations into AN1792-associated meningoencephalitis

BACKGROUND

In a phase 2a clinical trial of AN1792 (Study 201), a potential immunotherapeutic agent for use in Alzheimer's disease (AD), approximately 6% of the treated AD patients (18/300) developed meningoencephalitis (ME).

OBJECTIVE

To elucidate potential immune mechanisms of treatment-induced ME.

METHODS

Peripheral blood mononuclear cells obtained from patients who received AN1792 were stimulated in vitro either with beta-amyloid (Abeta) or various overlapping peptides of Abeta(1-42), followed by quantification of cytokine-secreting cells by enzyme-linked immunosorbent spot assay.

RESULTS

A significant difference in the quality of the T-cell responses between patients in Study 201 and those in earlier studies of AN1792 was noted. T-cell responses specific to the carboxy terminus of Abeta elicited from patients' peripheral blood mononuclear cells in an earlier multiple dose study (Study 102) were Th2 biased, while those from Study 201 were biased toward a proinflammatory Th1 response. Antibody responses in both studies were quantitatively and qualitatively similar (as determined by epitope mapping). The addition of polysorbate 80 to the formulation used in Study 201 is the most likely explanation for the difference in the T-cell response.

CONCLUSION

ME following injection of AN1792 may be related to immune response differences driven by a formulation change. To address this, a novel peptide-carrier protein conjugate using an amino-terminal fragment of Abeta (ACC-001) has been developed to avoid potentially harmful T-cell responses, while maintaining a similar antibody response to that of AN1792. Immunotherapeutic trials using this treatment approach in AD patients are in progress.

Red blood cells are the major source of alpha-synuclein in blood

BACKGROUND

Alpha-synuclein has been directly linked to Parkinson's disease etiology by mutations in and multiplication of its gene that result in a familial form of Parkinson's disease. Alpha-synuclein has been detected in blood, and was found to be elevated in the blood of those individuals with the alpha-synuclein gene multiplication.

OBJECTIVE

A complete analysis of the level of alpha-synuclein in blood has not been performed. In this report, we determine the quantitative distribution of alpha-synuclein in the plasma and different cellular fractions of human blood. The levels of alpha-synuclein in human and mouse blood are compared.

METHODS

Alpha-synuclein levels in the different fractions of blood were quantified by a sandwich ELISA with purified recombinant alpha-synuclein as an assay standard. Samples were further characterized by Western immunoblot analysis.

RESULTS

More than 99% of the alpha-synuclein resides in the red blood cells (RBCs) with less than 1% of the total detected in the plasma, platelets and peripheral blood mononuclear cells.

CONCLUSIONS

More than 99% of the alpha-synuclein in human blood is present in the peripheral blood cells, with the remainder in plasma. Fractionation of peripheral blood cells from human blood and quantification of alpha-synuclein revealed that only a very small amount of the total alpha-synuclein is present in peripheral blood mononuclear cells, and platelets, with the majority of alpha-synuclein in blood being present in RBCs. Considering the abundance and fragility of RBCs, alpha-synuclein levels in these other blood fractions or other bodily fluids such as cerebrospinal fluid may be artificially elevated by contamination with intact or lysed RBCs.

Effect of statins on Alzheimer's disease biomarkers in cerebrospinal fluid

BACKGROUND

Treatment with HMG-CoA reductase inhibitors ("statins") has been variably associated with a reduced risk of Alzheimer's disease (AD) in epidemiologic studies and reduced amyloid-beta (Abeta) deposition in animal models of AD. Putative neuroprotective effects of statins may vary in relation to their ability to penetrate into the central nervous system (CNS).

METHODS

We measured levels of cerebrospinal fluid (CSF) AD biomarkers following 14 weeks of treatment with simvastatin (a CNS permeant statin; n=10) at 40 mg/day or pravastatin (a CNS impermeant statin; n=13) at 80 mg/day in hypercholesterolemic subjects without dementia.

RESULTS

Simvastatin, but not pravastatin, reduced CSF levels of phospho-tau-181 (p-tau181) in all subjects. There were no differences in CSF levels of total tau, Abeta42, Abeta40, soluble amyloid beta protein precursor (sAbetaPP) alpha or beta, or F2-isoprostanes.

CONCLUSIONS

Statins may modulate the phosphorylation of tau in humans and this effect may depend on the CNS availability of the statin. These results suggest another mechanism by which statins may act to reduce the risk of AD.

Abeta species removal after abeta42 immunization

Neuropathologic examination of 3 patients with Alzheimer disease in the Elan Pharmaceuticals trial using antibodies specific for different Abeta species showed in one case, 4 months after the immunization, evidence of a stage of active plaque clearance with "moth-eaten" plaques and abundant Abeta phagocytosis by microglia. At 1 to 2 years after immunization, 2 cases showed extensive areas cleared of plaques (69% and 86% of the temporal cortex was plaque-free). Cortex cleared of plaques in all 3 cases had a characteristic constellation of features, including a very low plaque burden, sparse residual dense plaque cores, and phagocytosed Abeta within microglia. There was resolution of tau-containing dystrophic neurites, although other features of tau pathology (tangles and neuropil threads) remained and cerebral amyloid angiopathy persisted. Although most antibodies generated by Abeta42 immunization in humans bind the intact N-terminus, immunohistochemistry with specific antibodies showed clearance of all major species of Abeta (Abeta40, Abeta42, and N-terminus truncated Abeta). Abeta immunotherapy can clear all Abeta species from the cortex. However, if it is to be used for treatment of established Alzheimer disease, then the residual tau pathology and cerebral amyloid angiopathy require further study.

Increased T cell recruitment to the CNS after amyloid beta 1-42 immunization in Alzheimer's mice overproducing transforming growth factor-beta 1

Immunotherapy targeting the amyloid beta (Abeta) peptide is a novel therapy under investigation for the treatment of Alzheimer's disease (AD). A clinical trial using Abeta(1-42) (AN1792) as the immunogen was halted as a result of development of meningoencephalitis in a small number of patients. The cytokine TGF-beta1 is a key modulator of immune responses that is increased in the brain in AD. We show here that local overexpression of TGF-beta1 in the brain increases both meningeal and parenchymal T lymphocyte number. Furthermore, TGF-beta1 overexpression in a mouse model for AD [amyloid precursor protein (APP) mice] leads to development of additional T cell infiltrates when mice were immunized at a young but not old age with AN1792. Notably, only mice overproducing both Abeta (APP mice) and TGF-beta1 experienced a rise in T lymphocyte number after immunization. One-third of infiltrating T cells were CD4 positive. We did not observe significant differences in B lymphocyte numbers in any of the genotypes or treatment groups. These results demonstrate that TGF-beta1 overproduction in the brain can promote T cell infiltration, in particular after Abeta(1-42) immunization. Likewise, levels of TGF-beta1 or other immune factors in brains of AD patients may influence the response to Abeta(1-42) immunization.

Mice as models: transgenic approaches and Alzheimer's disease

Progress in understanding and treating Alzheimer's disease (AD) has been tremendously bolstered by the era of transgenic models of AD. The identification of disease-causing mutations in proteins such as amyloid-beta precursor protein (betaAPP) and presenilin1 (PS1), together with the discovery of other high risk factors (e.g., Apolipoprotein E4), as well as pathogenic mutations in the tau protein has led to the creation of several transgenic mice, including those expressing bi- and tri-genic constructs. Each model has unique pathologies that provide insights into disease mechanisms and interactive features of neuropathologic cascades. More importantly, therapeutic hypotheses are now testable in a manner unheard of less than 15 years ago. The wealth of new approaches currently in clinical and preclinical evaluations can be directly attributed to the impact of these animals on our ability to model relevant aspects of the disease. As a result, we may see containment or even the elimination of AD in the near future as a direct consequence of these advances.

Phosphorylation of Ser-129 Is the Dominant Pathological Modification of α-Synuclein in Familial and Sporadic Lewy Body Disease

A comprehensive, unbiased inventory of synuclein forms present in Lewy bodies from patients with dementia with Lewy bodies was carried out using two-dimensional immunoblot analysis, novel sandwich enzyme-linked immunosorbent assays with modification-specific synuclein antibodies, and mass spectroscopy. The predominant modification of alpha-synuclein in Lewy bodies is a single phosphorylation at Ser-129. In addition, there is a set of characteristic modifications that are present to a lesser extent, including ubiquitination at Lys residues 12, 21, and 23 and specific truncations at Asp-115, Asp-119, Asn-122, Tyr-133, and Asp-135. No other modifications are detectable by tandem mass spectrometry mapping, except for a ubiquitous N-terminal acetylation. Small amounts of Ser-129 phosphorylated and Asp-119-truncated alpha-synuclein are present in the soluble fraction of both normal and disease brains, suggesting that these Lewy body-associated forms are produced during normal metabolism of alpha-synuclein. In contrast, ubiquitination is only detected in Lewy bodies and is primarily present on phosphorylated synuclein; it therefore likely occurs after phosphorylated synuclein has deposited into Lewy bodies. This invariant pattern of specific phosphorylation, truncation, and ubiquitination is also present in the detergent-insoluble fraction of brain from patients with familial Parkinson's disease (synuclein A53T mutation) as well as multiple system atrophy, suggesting a common pathogenic pathway for both genetic and sporadic Lewy body diseases. These observations are most consistent with a model in which preferential accumulation of normally produced Ser-129 phosphorylated alpha-synuclein is the key event responsible for the formation of Lewy bodies in various Lewy body diseases.

A beta immunotherapy: Lessons learned for potential treatment of Alzheimer's disease

Amyloid-beta (A beta) immunotherapy for treatment of Alzheimer's disease (AD) was first described in 1999 and has been very informative regarding the role of A beta in AD. Through the efforts of many laboratories we now know that it is possible to reduce amyloid burden and many related AD pathologies in numerous animal models of the disease. Furthermore, initial clinical testing with AN1792, composed of A beta(1-42 )and an adjuvant, has yielded very important insights into both the clinical potential of the approach and the impact of A beta peptide on the disease. A brief review of our current understanding of A beta immunotherapy is described. These findings have led to newer alternative A beta immunotherapy approaches that include both active and passive approaches that are currently in clinical testing in both the USA and Europe.

Distribution of Abeta peptide in whole blood

The measurement of amyloid beta peptides (Abeta) in blood and plasma is expected to be a useful biomarker as potential therapeutics designed to lower Abeta peptide enter clinical trials. Many reports have suggested that Abeta could bind to substances in blood that may influence the recovery of Abeta peptide in plasma, its detection by conventional ELISAs or the actual turnover and half-life of the peptide in blood. In this study we describe a process for analyzing total Abeta in whole blood and plasma using denaturing solid-phase extraction followed by reverse-phase HPLC linked to ELISA. Comparison of total Abeta peptide levels in whole blood and plasma from the same bleed showed that most of the Abeta peptide is captured in the plasma if the samples are first denatured. In contrast, plasma that was assayed without denaturation could show greater than 70% reduction in apparent total Abeta peptide. This suggested that there was a pool of Abeta peptide in non-denatured plasma that is occluded from detection by ELISA, perhaps by binding to plasma proteins.

Beta-amyloid immunotherapy prevents synaptic degeneration in a mouse model of Alzheimer's disease

Alzheimer's disease neuropathology is characterized by key features that include the deposition of the amyloid beta peptide (Abeta) into plaques, the formation of neurofibrillary tangles, and the loss of neurons and synapses in specific brain regions. The loss of synapses, and particularly the associated presynaptic vesicle protein synaptophysin in the hippocampus and association cortices, has been widely reported to be one of the most robust correlates of Alzheimer's disease-associated cognitive decline. The beta-amyloid hypothesis supports the idea that Abeta is the cause of these pathologies. However, the hypothesis is still controversial, in part because the direct role of Abeta in synaptic degeneration awaits confirmation. In this study, we show that Abeta reduction by active or passive Abeta immunization protects against the progressive loss of synaptophysin in the hippocampal molecular layer and frontal neocortex of a transgenic mouse model of Alzheimer's disease. These results, substantiated by quantitative electron microscopic analysis of synaptic densities, strongly support a direct causative role of Abeta in the synaptic degeneration seen in Alzheimer's disease and strengthen the potential of Abeta immunotherapy as a treatment approach for this disease.

Abeta vaccination effects on plaque pathology in the absence of encephalitis in Alzheimer disease

The authors report a patient with Alzheimer disease (AD) without encephalitis who was immunized with AN-1792 (an adjuvanted formulation of Abeta-42). There were no amyloid plaques in the frontal cortex and abundant Abeta-immunoreactive macrophages, but tangles and amyloid angiopathy were present. The white matter appeared normal and minimal lymphocytic infiltration in the leptomeninges was observed. This case illustrates the effects of an Abeta-based immunization on AD pathogenesis in the absence of overt meningoencephalitis and leukoencephalopathy.

Effects of alpha-synuclein immunization in a mouse model of Parkinson's disease

Abnormal folding of alpha-synuclein (alpha-syn) is thought to lead to neurodegeneration and the characteristic symptoms of Lewy body disease (LBD). Since previous studies suggest that immunization might be a potential therapy for Alzheimer's disease, we hypothesized that immunization with human (h)alpha-syn might have therapeutic effects in LBD. For this purpose, halpha-syn transgenic (tg) mice were vaccinated with halpha-syn. In mice that produced high relative affinity antibodies, there was decreased accumulation of aggregated halpha-syn in neuronal cell bodies and synapses that was associated with reduced neurodegeneration. Furthermore, antibodies produced by immunized mice recognized abnormal halpha-syn associated with the neuronal membrane and promoted the degradation of halpha-syn aggregates, probably via lysosomal pathways. Similar effects were observed with an exogenously applied FITC-tagged halpha-syn antibody. These results suggest that vaccination is effective in reducing neuronal accumulation of halpha-syn aggregates and that further development of this approach might have a potential role in the treatment of LBD.

Amyloid-beta neurotoxicity is mediated by FISH adapter protein and ADAM12 metalloprotease activity

Based on a variety of genetic, biochemical, and neuropathological evidence, amyloid-beta peptide (Abeta) has been suggested to be causal in Alzheimer's disease (AD). Abeta has been shown to mediate neurodegenerative and inflammatory changes associated with amyloid plaques, as well as exert direct neurotoxicity through oligomeric forms of Abeta. The mechanism of Abeta toxicity, however, remains largely unknown. In this work, we show that an early event after exposure of postmitotic neurons to Abeta is tyrosine phosphorylation of FISH adapter protein. FISH binds to and potentially regulates certain ADAM family members. We present evidence that FISH and ADAM12 mediate the neurotoxic effect of Abeta. Expression of an ADAM12 protease-deficient mutant (ADAM12DeltaMP) blocks Abeta-induced neuronal death, and expression of an N-terminal fragment of FISH reduces Abeta toxicity. The C-terminal fragment of FISH containing the ADAMs binding region is found to be sufficient for induction of neuronal death, which is prevented by coexpression of the ADAM12DeltaMP. Abeta treatment, as well as expression of the C-terminal toxic FISH fragment, induces accumulation of ADAM12 N-terminal cleavage product in conditioned medium, demonstrating activation of the ADAM metalloprotease/sheddase activity. ADAM12 protein is reduced in AD brains, pointing to a possible increase in ADAM12 proteolytic activity. These data suggest that Abeta toxicity is mediated by FISH and ADAM12 and may provide insights into therapeutic strategies for AD treatment.

Aβ42 immunization in Alzheimer's disease generates Aβ N-terminal antibodies

Serum samples from Alzheimer's disease (AD) patients immunized with Abeta42 (AN1792) were analyzed to determine the induced antibody properties including precise amyloid-beta peptide (Abeta) epitopes and amyloid plaque-binding characteristics. The predominant response in these patients is independent of whether or not meningoencephalitis developed and is against the free amino terminus of Abeta. The immunostaining of amyloid plaques in brain tissue by patient sera is adsorbable by a linear Abeta1-8 peptide, demonstrating that the antibodies are directed predominantly to this epitope and not dependent on Abeta conformations or aggregates specific to plaques. Furthermore, the antibodies are not capable of binding amyloid precursor protein and would be predicted to be competent in facilitating clearance of amyloid plaques in AD brains.

Current progress in beta-amyloid immunotherapy

As neuroscientists, we are taught that the brain is immune privileged and thus unlikely to be affected by the peripheral immune system. Accordingly, initial results demonstrating the effectiveness of beta-amyloid (Abeta) immunotherapy in mouse models of Alzheimer's disease (AD) were viewed with considerable surprise and some skepticism. Many groups have since demonstrated efficacy with Abeta immunotherapy in models of AD, using Abeta-based immunogens and anti-Abeta antibodies. Clinical trials involving Abeta immunotherapy for AD are in progress and are providing a wealth of information around the amyloid hypothesis of AD. Abeta immunotherapy is also raising new opportunities and questions about the general role of the immune system in neurodegenerative diseases.

Morphological characterization of Thioflavin-S-positive amyloid plaques in transgenic Alzheimer mice and effect of passive Abeta immunotherapy on their clearance

Transgenic mice mimicking certain features of Alzheimer's disease (AD)-pathology, namely amyloid plaques and neurofibrillary tangles, have been developed in an effort to better understand the mechanism leading to the formation of these characteristic cerebral lesions. More recently, these animal models have been widely used to investigate emergent therapies aimed at the reduction of the cerebral amyloid load. Several studies have shown that immunotherapy targeting the amyloid peptide (Abeta) is efficacious at clearing the amyloid plaques or preventing their formation, and at reducing the memory/behavior impairment observed in these animals. In AD, different types of plaques likely have different pathogenic significance, and further characterization of plaque pathology in the PDAPP transgenic mice would enhance the evaluation of potential therapeutics. In the present study, a morphological classification of amyloid plaques present in the brains of PDAPP mice was established by using Thioflavin-S staining. Neuritic dystrophy associated with amyloid plaques was also investigated. Finally, the efficacy of passive immunization with anti-Abeta antibodies on the clearance of Thio-S positive amyloid plaques was studied. Our results show that distinct morphological types of plaques are differentially cleared depending upon the isotype of the antibody.

Epitope and isotype specificities of antibodies to beta -amyloid peptide for protection against Alzheimer's disease-like neuropathology

Transgenic PDAPP mice, which express a disease-linked isoform of the human amyloid precursor protein, exhibit CNS pathology that is similar to Alzheimer's disease. In an age-dependent fashion, the mice develop plaques containing beta-amyloid peptide (Abeta) and exhibit neuronal dystrophy and synaptic loss. It has been shown in previous studies that pathology can be prevented and even reversed by immunization of the mice with the Abeta peptide. Similar protection could be achieved by passive administration of some but not all monoclonal antibodies against Abeta. In the current studies we sought to define the optimal antibody response for reducing neuropathology. Immune sera with reactivity against different Abeta epitopes and monoclonal antibodies with different isotypes were examined for efficacy both ex vivo and in vivo. The studies showed that: (i) of the purified or elicited antibodies tested, only antibodies against the N-terminal regions of Abeta were able to invoke plaque clearance; (ii) plaque binding correlated with a clearance response and neuronal protection, whereas the ability of antibodies to capture soluble Abeta was not necessarily correlated with efficacy; (iii) the isotype of the antibody dramatically influenced the degree of plaque clearance and neuronal protection; (iv) high affinity of the antibody for Fc receptors on microglial cells seemed more important than high affinity for Abeta itself; and (v) complement activation was not required for plaque clearance. These results indicate that antibody Fc-mediated plaque clearance is a highly efficient and effective process for protection against neuropathology in an animal model of Alzheimer's disease.

Non-Fc-mediated mechanisms are involved in clearance of amyloid-beta in vivo by immunotherapy

Transgenic (Tg) mouse models overexpressing amyloid precursor protein (APP) develop senile plaques similar to those found in Alzheimer's disease in an age-dependent manner. Recent reports demonstrated that immunotherapy is effective at preventing or removing amyloid-beta deposits in the mouse models. To characterize the mechanisms involved in clearance, we used antibodies of either IgG1 (10d5) or IgG2b (3d6) applied directly to the brains of 18-month-old Tg2576 or 20-month-old PDAPP mice. Both 10d5 and 3d6 led to clearance of 50% of diffuse amyloid deposits in both animal models within 3 d. Fc receptor-mediated clearance has been shown to be important in an ex vivo assay showing antibody-mediated clearance of plaques by microglia. We now show, using in vivo multiphoton microscopy, that FITC-labeled F(ab')2 fragments of 3d6 (which lack the Fc region of the antibody) also led to clearance of 45% of the deposits within 3 d, similar to the results obtained with full-length 3d6 antibody. This result suggests that direct disruption of plaques, in addition to Fc-dependent phagocytosis, is involved in the antibody-mediated clearance of amyloid-beta deposits in vivo. Dense-core deposits that were not cleared were reduced in size by approximately 30% with full-length antibodies and F(ab')2 fragments 3 d after a topical treatment. Together, these results indicate that clearance of amyloid deposits in vivo may involve, in addition to Fc-dependent clearance, a non-Fc-mediated disruption of plaque structure.

Immunotherapy with beta-amyloid for Alzheimer's disease: a new frontier

Alzheimer's disease (AD) represents the fourth leading cause of death in the U.S. and the leading cause of dementia in the elderly population. Until recently, there was little hope of finding a way to prevent the underlying brain pathology from progressing toward the inevitable conclusion of the disease. However, new immunotherapeutic approaches have been described that are based on vaccination with the beta-amyloid 1-42 peptide (Abeta). The encouraging efficacy and safety of Abeta immunization in reducing neuropathology in animal models of AD has opened up new therapeutic possibilities for patients. Immunization with Abeta is aimed at reducing the Abeta-associated pathology of AD. It is hypothesized that this approach will also reduce the cascade of downstream events leading to neuronal cell loss and, ultimately, dementia. The ensuing articles in this issue describe various aspects of the Abeta immunization strategy and their potential relevance to AD treatment.

Potential treatment opportunities for Alzheimer's disease through inhibition of secretases and Abeta immunization

Research over the past ten years on Alzheimer's disease has pursued many opportunities. Notable amongst the various approaches are efforts related to the "amyloid hypothesis." This hypothesis posits that the beta amyloid peptide causes the extensive neuropathology and clinical decline associated with the disease. Extensive research in this area has shown that the beta amyloid peptide is produced by proteases termed "secretases" and it has been shown that blockade of secretase functions reduce the amount of beta amyloid peptide produced. An additional approach to reduce beta amyloid, through an increase in clearance mechanisms, is to immunize with the peptide itself and induce an antibody response. The specifically elicited antibodies then bind to and stimulate clearance of the peptide from the brain. These findings have stimulated several approaches to develop novel therapeutic strategies to treat Alzheimer's disease that either are about or have entered the clinic.

Encapsulation in biodegradable microparticles enhances serum antibody response to parenterally-delivered beta-amyloid in mice

Poly(lactide-co-glycolide) (PLG) microspheres were tested as a parenteral delivery system for human beta-amyloid (1-42) (Abeta), a potential immunotherapeutic undergoing assessment in Phase 1 studies for Alzheimer's disease (AD). Abeta was successfully encapsulated in PLG microspheres of average sizes of 3 or 15 microm diameter. Swiss Webster (SW) mice were injected by the sub-cutaneous (s.c.) or intra-peritoneal (i.p.) routes with 3-33 microg Abeta. Abeta-PLG microparticles (3 microm) induced dose-dependent antibody responses, which were maximal at 33 microg Abeta, while Abeta in phosphate-buffered saline (PBS) produced weak antibody responses at the same doses by both routes. Significantly increased antibody responses were seen for both small and large particle formulations given by the i.p. route in comparison to the s.c route. It was previously reported that passive immunisation with Abeta-specific antibodies cleared amyloid plaques in a mouse model of AD (Bard F, Cannon C, Barbour R, et al. Peripherally administered antibodies against amyloid beta-peptide enter the nervous system and reduce pathology in a mouse model of Alzheimer disease. Nature Med 2000;6:916-19), an indication that induction of serum antibody is a prerequisite for efficacy.

Prevention and reduction of AD-type pathology in PDAPP mice immunized with A beta 1-42

In AD certain brain structures contain a pathological density of A beta protein deposited into plaques. The effect of genetic mutations found in early onset AD patients was an overproduction of A beta 42, strongly suggesting that overproduction of A beta 42 is associated with AD. We hypothesized that an immunological response to A beta 42 might alter its turnover and metabolism. Young PDAPP transgenic mice were immunized with A beta 1-42, which essentially prevented amyloid deposition; astrocytosis was dramatically reduced and there was reduction in A beta-induced inflammatory response as well. A beta 1-42 immunization also appeared to arrest the progression of amyloidosis in older PDAPP mice. A beta immunization appears to increase clearance of amyloid plaques, and may therefore be a novel and effective approach for the treatment of AD.

Peripherally administered antibodies against amyloid beta-peptide enter the central nervous system and reduce pathology in a mouse model of Alzheimer disease

One hallmark of Alzheimer disease is the accumulation of amyloid beta-peptide in the brain and its deposition as plaques. Mice transgenic for an amyloid beta precursor protein (APP) mini-gene driven by a platelet-derived (PD) growth factor promoter (PDAPP mice), which overexpress one of the disease-linked mutant forms of the human amyloid precursor protein, show many of the pathological features of Alzheimer disease, including extensive deposition of extracellular amyloid plaques, astrocytosis and neuritic dystrophy. Active immunization of PDAPP mice with human amyloid beta-peptide reduces plaque burden and its associated pathologies. Several hypotheses have been proposed regarding the mechanism of this response. Here we report that peripheral administration of antibodies against amyloid beta-peptide, was sufficient to reduce amyloid burden. Despite their relatively modest serum levels, the passively administered antibodies were able to enter the central nervous system, decorate plaques and induce clearance of preexisting amyloid. When examined in an ex vivo assay with sections of PDAPP or Alzheimer disease brain tissue, antibodies against amyloid beta-peptide triggered microglial cells to clear plaques through Fc receptor-mediated phagocytosis and subsequent peptide degradation. These results indicate that antibodies can cross the blood-brain barrier to act directly in the central nervous system and should be considered as a therapeutic approach for the treatment of Alzheimer disease and other neurological disorders.

Purification and cloning of amyloid precursor protein beta-secretase from human brain

Proteolytic processing of the amyloid precursor protein (APP) generates amyloid beta (Abeta) peptide, which is thought to be causal for the pathology and subsequent cognitive decline in Alzheimer's disease. Cleavage by beta-secretase at the amino terminus of the Abeta peptide sequence, between residues 671 and 672 of APP, leads to the generation and extracellular release of beta-cleaved soluble APP, and a corresponding cell-associated carboxy-terminal fragment. Cleavage of the C-terminal fragment by gamma-secretase(s) leads to the formation of Abeta. The pathogenic mutation K670M671-->N670L671 at the beta-secretase cleavage site in APP, which was discovered in a Swedish family with familial Alzheimer's disease, leads to increased beta-secretase cleavage of the mutant substrate. Here we describe a membrane-bound enzyme activity that cleaves full-length APP at the beta-secretase cleavage site, and find it to be the predominant beta-cleavage activity in human brain. We have purified this enzyme activity to homogeneity from human brain using a new substrate analogue inhibitor of the enzyme activity, and show that the purified enzyme has all the properties predicted for beta-secretase. Cloning and expression of the enzyme reveals that human brain beta-secretase is a new membrane-bound aspartic proteinase.

Effects of time and cholinesterase inhibitor treatment on multiple cerebrospinal fluid parameters in Alzheimer's disease

Development of neuropathology in Alzheimer's disease (AD) cannot be studied directly in living patients. Therefore, concentrations in cerebrospinal fluid (CSF) of the proteins tau, A beta 42, alpha 1-ACT, apoE and other molecules have been analyzed to elucidate their possible role in degeneration and as biomarkers of the disease. To date, however, studies have not analyzed multiple markers in the same patients over time and as a function of pharmacological interventions. In the present investigation we measured CSF tau, A beta 42, alpha 1-ACT, apoE, total protein and electrophoretic fractions, and leukocytes, as well as MMSE, in 12 AD patients of known APOE phenotype. Two or three CSF examinations were performed during periods of up to 2 1/2 years, while subjects were on and off treatment with the cholinesterase inhibitor (ChEI) metrifonate (MTF). CSF A beta 42 and tau levels were in agreement with clinical diagnosis of AD in all patients. Abnormally high proportions of monocytes were found in CSF at baseline, and these proportions correlated positively with plasma alpha 1-ACT and MMSE scores. A small but significant increase in CSF alpha 1-ACT, which correlated with peripheral alpha 1-ACT, was associated with 6 months' MTF treatment, though alpha 1-ACT levels did not change further when treatment continued for 2 years. Monocyte proportions in CSF declined over time in both treated and untreated patients. Among 5 of 6 patients treated for 2 years or more with MTF, CSF measures remained relatively stable. One patient had changes in CSF parameters apparently associated with a transient ischemic attack. Our findings did not indicate that slowed cognitive decline with MTF treatment is associated with systematic change in any CSF marker analyzed. The results suggest that further investigations of the relationship of tau, A beta 42 and cellular abnormalities in CSF early in the course of AD are warranted.

Longitudinal stability of CSF tau levels in Alzheimer patients

BACKGROUND

Antemortem levels of tau in the cerebrospinal fluid (CSF) of Alzheimer's disease (AD) patients have repeatedly been demonstrated to be elevated when compared to controls. Although CSF tau has been reported to be elevated even in very mild AD, it is unknown how tau levels change during the course of the disease.

METHODS

We have followed 29 mild-to-moderately affected AD subjects over 2 years with repeated CSF taps. Clinical measures of dementia severity (Clinical Dementia Rating Scale, Global Deterioration Scale and Mini-Mental Status Examination) were obtained at the start and conclusion of the observation period, and CSF tau was measured with a standard enzyme-linked immunoabsorbent assay (ELISA) using two monoclonal antibodies.

RESULTS

Despite significant changes in the clinical measures consistent with progression of the disease, no significant overall change in CSF tau levels (548 +/- 355 vs. 557 +/- 275 pg/mL, NS) was observed. None of the clinical variables was significantly correlated with either baseline measures of CSF tau or delta CSF tau (last-first). Similarly, CSF tau at baseline and changes over time were not significantly related to Apolipoprotein E (APO E) phenotype.

CONCLUSIONS

These data suggest that CSF tau levels are stable over extended periods of time in a group of mild-to-moderately demented AD subjects and that CSF tau levels do not predict the severity or rate of progression of AD, at least not during the middle stages of the illness.

Alterations in synaptic transmission and long-term potentiation in hippocampal slices from young and aged PDAPP mice

Synaptic transmission and plasticity were studied in the CA1 field of hippocampal slices from young and aged transgenic mice over-expressing a mutant form of the human amyloid precursor protein (PDAPP mice). The transgenic mice at 4-5 months of age, prior to the formation of amyloid-beta peptide deposits in these animals, differed from non-transgenic control mice in three respects: (1) paired-pulse facilitation (PPF) was enhanced; (2) responses to high frequency stimulation bursts were distorted; (3) long-term potentiation (LTP) decayed more rapidly. More striking was the profound reduction in the size of synaptic responses and frequent loss of field potentials that were found in the transgenic mice at 27-29 months, an age at which they exhibit numerous amyloid plaques, neuritic dystrophy, and gliosis. Control mice at these ages did not show such dramatic effects. PPF was reduced in aged transgenic mice, compared to aged controls; however, LTP was still in evidence, although direct comparisons of its induction conditions in aged transgenic and control mice were compromised by the profound differences in field potentials between the two groups. These results point to two conclusions: (1) altered synaptic communication appears in PDAPP mice in advance of amyloid plaque formation and probably involves changes in presynaptic calcium kinetics; (2) the disturbances in synaptic transmission that appear when abundant plaques and Alzheimer's-like neuropathology are present in the transgenic mice are not necessarily accompanied by a disproportionate loss of long-term synaptic plasticity.

Immunization with amyloid-beta attenuates Alzheimer-disease-like pathology in the PDAPP mouse

Amyloid-beta peptide (Abeta) seems to have a central role in the neuropathology of Alzheimer's disease (AD). Familial forms of the disease have been linked to mutations in the amyloid precursor protein (APP) and the presenilin genes. Disease-linked mutations in these genes result in increased production of the 42-amino-acid form of the peptide (Abeta42), which is the predominant form found in the amyloid plaques of Alzheimer's disease. The PDAPP transgenic mouse, which overexpresses mutant human APP (in which the amino acid at position 717 is phenylalanine instead of the normal valine), progressively develops many of the neuropathological hallmarks of Alzheimer's disease in an age- and brain-region-dependent manner. In the present study, transgenic animals were immunized with Abeta42, either before the onset of AD-type neuropathologies (at 6 weeks of age) or at an older age (11 months), when amyloid-beta deposition and several of the subsequent neuropathological changes were well established. We report that immunization of the young animals essentially prevented the development of beta-amyloid-plaque formation, neuritic dystrophy and astrogliosis. Treatment of the older animals also markedly reduced the extent and progression of these AD-like neuropathologies. Our results raise the possibility that immunization with amyloid-beta may be effective in preventing and treating Alzheimer's disease.

Presenilin 1 regulates the processing of beta-amyloid precursor protein C-terminal fragments and the generation of amyloid beta-protein in endoplasmic reticulum and Golgi

Progressive cerebral deposition of the amyloid beta-protein (Abeta) is believed to play a pivotal role in the pathogenesis of Alzheimer's disease (AD). The highly amyloidogenic 42-residue form of Abeta (Abeta42) is the first species to be deposited in both sporadic and familial AD. Mutations in two familial AD-linked genes, presenilins 1 (PS1) and 2 (PS2), selectively increase the production of Abeta42 in cultured cells and the brains of transgenic mice, and gene deletion of PS1 shows that it is required for normal gamma-secretase cleavage of the beta-amyloid precursor protein (APP) to generate Abeta. To establish the subcellular localization of the PS1 regulation of APP processing to Abeta, fibroblasts from PS1 wild-type (wt) or knockout (KO) embryos as well as Chinese hamster ovary (CHO) cells stably transfected with wt or mutant PS1 were subjected to subcellular fractionation on discontinuous Iodixanol gradients. APP C-terminal fragments (CTF) were markedly increased in both endoplasmic reticulum- (ER-) and Golgi-rich fractions of fibroblasts from KO mice; moreover, similar increases were documented directly in KO brain tissue. No change in the subcellular distribution of full-length APP was detectable in fibroblasts lacking PS1. In CHO cells, a small portion of APP, principally the N-glycosylated isoform, formed complexes with PS1 in both ER- and Golgi-rich fractions, as detected by coimmunoprecipitation. When the same fractions were analyzed by enzyme-linked immunosorbent assays for Abetatotal and Abeta42, Abeta42 was the major Abeta species in the ER fraction (Abeta42:Abetatotal ratio 0.5-1.0), whereas absolute levels of both Abeta42 and Abeta40 were higher in the Golgi fraction and the Abeta42:Abetatoal ratio was 0.05-0.16 there. Mutant PS1 significantly increased Abeta42 levels in the Golgi fraction. Our results indicate PS1 and APP can interact in the ER and Golgi, where PS1 is required for proper gamma-secretase processing of APP CTFs, and that PS1 mutations augment Abeta42 levels principally in Golgi-like vesicles.

Apolipoprotein E epsilon 4 allele in association with global cognitive performance and CSF markers in Alzheimer's disease

To better define the influence of apolipoprotein E (ApoE) epsilon 4 genotype on the cognitive and biochemical features of Alzheimer's disease (AD), cross-sectional analysis of global cognitive measures and cerebrospinal fluid studies gathered on AD subjects at a tertiary care facility between 1986 and 1997 was carried out. The 112 AD patients examined included 62 women and 50 men with a mean (SD) age of 64.2 (9.2) years. Patient demographics; illness onset age and duration, education level and global cognitive measures were recorded systematically. Genetic analysis for ApoE allele type and biochemical characterization of CSF, including total tau concentration, was performed. Descriptive statistics of demographics, cognitive and CSF measures were performed by chi-square, ANOVA and Tukey's tests. Overrepresentation of the epsilon 4 allele was found, with 45.5% of AD patients heterozygous and 20.5% homozygous for ApoE epsilon 4. Overall, ApoE epsilon 4 status had no effect on mean onset age of AD (F = 1.56; p = 0.214), but an earlier mean onset age of AD (F = 4.10; p = 0.02) was seen in the late-onset subjects. No differences were found with regard to ApoE epsilon 4 status and measures of disease, duration of illness or global cognitive performance. Although CSF tau was elevated in our sample (575.4 +/- 290.3 pg/ml), ApoE epsilon 4 status did not influence total CSF tau or neurotransmitter metabolite levels. ApoE epsilon 4 genotype had no impact on a variety of illness severity, cognitive and CSF examinations in the largest cross-sectional analysis of AD subjects yet reported.

Cerebrospinal fluid tau protein is not elevated in HIV-associated neurologic disease in humans. HIV Neurobehavioral Research Center Group (HNRC)

We measured the concentrations of the neuron-specific protein, tau, in the cerebrospinal fluid (CSF) of 32 neurologically characterized HIV-infected (HIVpos) subjects and nine matched seronegative (HIVneg) controls using a sensitive ELISA assay. Of 32 HIVpos subjects, nine had HIV-associated neurocognitive disorders, and nine had clinically diagnosed peripheral neuropathies. CSF tau levels in subjects with HIV-associated neurocognitive disorders were similar to those in HIVneg subjects (185 +/- 83 vs. 223 +/- 106 pg/ml; P = 57). CSF tau levels in HIVpos subjects with peripheral neuropathies did not differ from those without neuropathies (320 +/- 190 vs. 251 +/- 185; P = 23). In summary, CSF tau levels were not elevated in patients with HIV-associated neurologic disease.

High cerebrospinal fluid tau and low amyloid beta42 levels in the clinical diagnosis of Alzheimer disease and relation to apolipoprotein E genotype

OBJECTIVE

To evaluate cerebrospinal fluid (CSF) levels of amyloid beta protein ending at amino acid 42 (Abeta42) and tau as markers for Alzheimer disease (AD) and to determine whether clinical variables influence these levels.

DESIGN

Cohort study.

SETTING

Six academic research centers with expertise in dementia.

SUBJECTS

Eighty-two patients with probable AD, including 24 with very mild dementia (Mini-Mental State Examination score >23/30) (AD group); 60 cognitively normal elderly control subjects (NC group); and 74 subjects with neurological disorders, including dementia (ND group).

MAIN OUTCOME MEASURES

Levels of Abeta42 and tau were compared among AD, NC, and ND groups. Relationships of age, sex, Mini-Mental State Examination score, and apolipoprotein E (Apo E) genotype with these levels were examined using multiple linear regression. Classification tree models were developed to optimize distinguishing AD from NC groups.

RESULTS

Levels of Abeta42 were significantly lower, and levels of tau were significantly higher, in the AD group than in the NC or ND group. In the AD group, Abeta42 level was inversely associated with Apo E epsilon4 allele dose and weakly related to Mini-Mental State Examination score; tau level was associated with male sex and 1 Apo E epsilon4 allele. Classification tree analysis, comparing the AD and NC subjects, was 90% sensitive and 80% specific. With specificity set at greater than 90%, the tree was 77% sensitive for AD. This tree classified 26 of 74 members of the ND group as having AD. They had diagnoses difficult to distinguish from AD clinically and a high Apo E epsilon4 allele frequency. Markers in CSF were used to correctly classify 12 of 13 patients who later underwent autopsy, including 1 with AD not diagnosed clinically.

CONCLUSIONS

Levels of CSF Abeta42 decrease and levels of CSF tau increase in AD. Apolipoprotein E epsilon4 had a dose-dependent relationship with CSF levels of Abeta42, but not tau. Other covariates influenced CSF markers minimally. Combined analysis of CSF Abeta42 and tau levels discriminated patients with AD, including patients with mild dementia, from the NC group, supporting use of these proteins to identify AD and to distinguish early AD from aging. In subjects in the ND group with an AD CSF profile, autopsy follow-up will be required to decide whether CSF results are false positive, or whether AD is a primary or concomitant cause of dementia.