Cerebrospinal Fluid Abeta42 Research Articles

Dynamics of Aβ Turnover and Deposition in Different β-Amyloid Precursor Protein Transgenic Mouse Models Following γ-Secretase Inhibition

Human beta-amyloid precursor protein (APP) transgenic mice are commonly used to test potential therapeutics for Alzheimer's disease. We have characterized the dynamics of beta-amyloid (Abeta) generation and deposition following gamma-secretase inhibition with compound LY-411575 [N(2)-[(2S)-2-(3,5-difluorophenyl)-2-hydroxyethanoyl]-N(1)-[(7S)-5-methyl-6-oxo-6,7-dihydro-5H-dibenzo[b,d]azepin-7-yl]-L-alaninamide]. Kinetic studies in preplaque mice distinguished a detergent-soluble Abeta pool in brain with rapid turnover (half-lives for Abeta40 and Abeta42 were 0.7 and 1.7 h) and a much more stable, less soluble pool. Abeta in cerebrospinal fluid (CSF) reflected the changes in the soluble brain Abeta pool, whereas plasma Abeta turned over more rapidly. In brain, APP C-terminal fragments (CTF) accumulated differentially. The half-lives for gamma-secretase degradation were estimated as 0.4 and 0.1 h for C99 and C83, respectively. Three different APP transgenic lines responded very similarly to gamma-secretase inhibition regardless of the familial Alzheimer's disease mutations in APP. Amyloid deposition started with Abeta42, whereas Abeta38 and Abeta40 continued to turn over. Chronic gamma-secretase inhibition lowered amyloid plaque formation to a different degree in different brain regions of the same mice. The extent was inversely related to the initial amyloid load in the region analyzed. No evidence for plaque removal below baseline was obtained. gamma-Secretase inhibition led to a redistribution of intracellular Abeta and an elevation of CTFs in neuronal fibers. In CSF, Abeta showed a similar turnover as in preplaque animals demonstrating its suitability as marker of newly generated, soluble Abeta in plaque-bearing brain. This study supports the use of APP transgenic mice as translational models to characterize Abeta-lowering therapeutics.

Cerebrospinal Fluid Biomarkers in Parkinson's Disease with Dementia and Dementia with Lewy Bodies

Clinical criteria for differentiating Parkinson's disease (PD) with dementia (PDD) from dementia with Lewy bodies (DLB) are unsatisfactory. Their existence as distinct clinicopathologic entities is still debated, although the burden of Alzheimer's disease (AD) pathology seems higher in DLB. Thus, analysis of cerebrospinal fluid (CSF) biomarkers (beta-amyloid(1-42) [Abeta42], total tau, and hyperphosphorylated tau [p-tau]) in living subjects might provide significant pathophysiological information on these diseases. Cerebrospinal fluid biomarkers were measured in DLB (n = 19), PDD (n = 18), and AD (n = 23) subjects matched for age, sex, and dementia severity, as well as in PD (n = 20) and normal control subjects (n = 20). DLB showed the lowest mean CSF Abeta42 levels, with a negative association to dementia duration (rho = -.42, p = .07). In DLB patients, mean CSF total tau levels were significantly lower than in AD patients (508 +/- 387 vs. 960 +/- 619, respectively) but twofold to threefold higher than in PDD (286 +/- 184), PD (160 +/- 64), or normal control subjects (177 +/- 76), with a positive association to dementia severity (Mini-Mental State Examination: rho = -.54, p = .02; Milan Overall Dementia Assessment: rho = -.66, p = .002). PDD patients had mean CSF Abeta42 and total tau levels similar to those seen in PD patients. Hyperphosphorylated tau was significantly increased in the AD group only. Cerebrospinal fluid Abeta42 and total tau have a different behavior in DLB and PDD, being related to duration and severity of dementia in DLB alone. Hyperphosphorylated tau is not significantly altered in these conditions.

Endocytosis Is Required for Synaptic Activity-Dependent Release of Amyloid-β In Vivo

Aggregation of amyloid-beta (Abeta) peptide into soluble and insoluble forms within the brain extracellular space is central to the pathogenesis of Alzheimer's disease. Full-length amyloid precursor protein (APP) is endocytosed from the cell surface into endosomes where it is cleaved to produce Abeta. Abeta is subsequently released into the brain interstitial fluid (ISF). We hypothesized that synaptic transmission results in more APP endocytosis, thereby increasing Abeta generation and release into the ISF. We found that inhibition of clathrin-mediated endocytosis immediately lowers ISF Abeta levels in vivo. Two distinct methods that increased synaptic transmission resulted in an elevation of ISF Abeta levels. Inhibition of endocytosis, however, prevented the activity-dependent increase in Abeta. We estimate that approximately 70% of ISF Abeta arises from endocytosis-associated mechanisms, with the vast majority of this pool also dependent on synaptic activity. These findings have implications for AD pathogenesis and may provide insights into therapeutic intervention.

Effects of Simvastatin on Cerebrospinal Fluid Biomarkers and Cognition in Middle-Aged Adults at Risk for Alzheimer's Disease

Statins reduce amyloid-beta (Abeta) levels in the brain and cerebrospinal fluid (CSF) in animals and may thereby favorably alter the pathobiology of AD. It is unclear if statins modify Abeta metabolism or improve cognition in asymptomatic middle-aged adults at increased risk for AD. In a 4-month randomized, double-blind, controlled study, we evaluated the effects of simvastatin 40 mg daily vs. placebo on CSF Abeta42 levels and cognition in 57 asymptomatic middle-aged adult children of persons with AD. Compared to placebo, individuals randomized to simvastatin for 4 months had similar changes in CSF Abeta42 (p=0.344) and total tau levels (p=0.226), yet greater improvements in some measures of verbal fluency (p=0.024) and working memory (p=0.015). APOE4 genotype, gender, and vascular risk factors were associated with CSF biomarker levels, but did not modify treatment effects. In asymptomatic middle-aged adults at increased risk for AD, simvastatin use improved selected measures of cognitive function without significantly changing CSF Abeta42 or total tau levels. Further studies are needed to clarify the impact of higher dose and/or longer duration statin therapy on not only Abeta metabolism, but also other preclinical processes related to the development of AD.

Infusion of Intravenous Immunoglobulin (IVIg) Containing anti-Abeta Antibodies is Associated with a Decrease of Abeta in Cerebrospinal Fluid (CSF) and Increase of Abeta in Blood from 8 Patients with Mild Alzheimer's Disease (AD)

Infusion of Intravenous Immunoglobulin (IVIg) Containing anti-Abeta Antibodies is Associated with a Decrease of Abeta in Cerebrospinal Fluid (CSF) and Increase of Abeta in Blood from 8 Patients with Mild Alzheimer's Disease (AD)

Therapeutic Potential of γ -Secretase Inhibitors and Modulators

According to the beta-amyloid (Abeta) hypothesis, compounds that inhibit gamma-secretase, the pivotal enzyme that generates Abeta, are potential therapeutics for Alzheimer's disease (AD). Studies in both transgenic and non-transgenic animal models of AD have indicated that gamma-secretase inhibitors, administered by the oral route, are able to lower brain Abeta concentrations. However, scanty data are available on the effects of these compounds on brain Abeta deposition after prolonged administration. Behavioral studies are also scarce with only one study indicating positive cognitive effects of a peptidomimetic compound (DAPT). Gamma-secretase inhibitors may cause abnormalities in the gastrointestinal tract, thymus and spleen in rodents. These toxic effects are likely due to inhibition of Notch cleavage, a transmembrane receptor involved in regulating cell-fate decisions. Interestingly, some non-steroidal anti-inflammatory drugs (NSAIDs) and other small organic molecules have been found to modulate gamma-secretase and to selectively reduce beta-amyloid(1-42) (Abeta42) levels without affecting Notch cleavage. Long-term histopathological and behavioral animal studies are available with these NSAIDs (mainly ibuprofen) but it is unclear if the observed in vivo effects on Abeta brain pathology and learning depend on their activity on gamma-secretase or on other biological targets. The first published clinical studies in healthy subjects and in AD patients with a gamma-secretase inhibitor, LY-450139, confirmed the dose-dependent inhibition of plasma Abeta but evidenced a later rebound in Abeta plasma levels and absence of a significant effect on cerebrospinal fluid Abeta concentrations. Some observed gastrointestinal adverse events have raised concerns. Clinical studies with other potent gamma-secretase inhibitors will tell us if these pharmacodynamic and tolerability profiles observed in humans are typical of the pharmacological class or are compound-specific. Given the uncertain Abeta reduction target and the potential for mechanism-based toxicity, it has been suggested that biomarkers for efficacy (cerebrospinal fluid Abeta42 levels) and toxicity (plasma adipsin levels) would be helpful in initial clinical trials with gamma-secretase inhibitors. A large ongoing Phase 3 study with (R)-flurbiprofen, a claimed selective Abeta42 lowering agent, will tell us if allosteric modulation of gamma-secretase is clinically effective.

The Relationship Between Cerebrospinal Fluid Biomarkers and Depression in Elderly Women

Cerebrospinal fluid (CSF) biomarkers including the 42 amino-acid form of beta-amyloid (Abeta42), total tau protein (T-tau), and the CSF/serum albumin ratio are markers of brain pathology and metabolism. Abeta42 and T-tau are sometimes used to discriminate geriatric depression from mild forms of Alzheimer disease (AD) in clinical studies. However, studies focusing on the relationship between these CSF biomarkers and geriatric depression are lacking. This was a cross-sectional study with a population-based sample of 84 nondemented elderly women in Sweden. Measurements included neuropsychiatric, physical, and lumbar puncture examinations, with Diagnostic and Statistical Manual of Mental Disorders, Third Revision-based depression diagnoses and measurement of CSF levels of Abeta42, T-tau, albumin, and serum albumin. Fourteen women (mean age: 72.6 years) had any depression (11 with major depressive disorder [MDD]). Compared to women without depression, women with MDD had higher levels of Abeta42 and the CSF/serum albumin ratio. The CSF/serum albumin ratio was also higher in women with any depression. No differences in T-tau were observed; however, T-tau increased with age. Higher levels of CSF Abeta42 were observed among elderly depressed women, in contrast to lower levels usually observed in AD, indicating potential neuropathological differences between the two disorders. Higher CSF/serum albumin ratios observed in depressed women point to potential vascular processes.

The normal equilibrium between CSF and plasma amyloid beta levels is disrupted in Alzheimer's disease

Amyloid-beta (Abeta) with 40 (Abeta40) and 42 (Abeta42) amino acids, the main components of amyloid plaques in the Alzheimer's disease (AD) brain, can be measured in human cerebrospinal fluid (CSF) and plasma. Whereas CSF Abeta42 is decreased in AD, some studies have reported changed plasma Abeta levels in AD and in subjects with mild cognitive impairment (MCI). To this date it is unclear if and how CSF and plasma levels of Abeta correlate with each other in healthy individuals, albeit earlier studies on AD patients found no correlation between CSF and plasma Abeta. We have measured Abeta40 and Abeta42 in paired CSF and plasma samples from patients with AD (n=39), MCI (n=29) and healthy control subjects (n=18). We observed a clear correlation between CSF and plasma levels for both Abeta40 and Abeta42 in healthy individuals, whereas no such correlation could be seen for AD or MCI cases. Similarly to other studies we also found low levels of Abeta42 in AD CSF, whereas there were no significant differences in plasma Abeta levels between the diagnostic groups. Our findings suggest that the normal equilibrium between CSF and plasma Abeta may be disrupted with the initiation of amyloid deposition in the brain.

Evaluation of CSF-Chlamydia pneumoniae, CSF-tau, and CSF-Abeta42 in Alzheimer’s disease and vascular dementia

The potential role of microbiological factors such as Chlamydia pneumoniae (ChP) in the pathogenesis of neurodegenerative disorders, including Alzheimer's disease (AD) and vascular dementia (VD), has been suggested, but the correctness of this hypothesis still needs to be tested. In this study the appearance of ChP in the cerebrospinal fluid (CSF) of 57 AD and 21 VD patients and in 47 controls (CG) as well as the influence of ChP on the levels of tau protein and Abeta42 were investigated. The frequency of ChP occurrence in the AD patient group (43.9%) was significantly higher (p < 0.001) than in the control group (10.6%). In the case of VD patients, 9.5% of this group was positive for ChP. The presence of ChP DNA in the CSF of patients with AD significantly increases the occurrence of this disease (odds ratio = 7.21). Cerebrospinal fluid Abeta42 levels were significantly lower in patients with AD than in the CG (p < 0.001). Cerebrospinal tau protein was significantly higher in AD vs. CG (p = 0.007). However, no relationships between the presence of the bacterium in CSF and the level of either tau or Abeta42 protein were observed. In conclusion, we may suspect that testing for the presence of ChP in CSF, along with the tau and Abeta42 markers, may be used in the clinic diagnosis of AD.

Low Serum Potassium in Mid Life Associated with Decreased Cerebrospinal Fluid Aβ42 in Late Life

Low serum potassium increases risk of hypertension and stroke, and cardiovascular factors increase the risk of Alzheimer disease (AD). We examined the association between serum potassium and the biologic marker cerebrospinal fluid amyloid-beta (Abeta42), which is decreased in Alzheimer disease patients. Psychiatric examinations, laboratory and other tests were conducted on a population-based sample of 1080 women aged 46 to 60 in 1968, with follow-ups in 1974, 1980, and 1992. In 1992, cerebrospinal fluid Abeta42 levels were obtained from 81 women. Increasing serum potassium in 1968 was associated with increasing cerebrospinal fluid Abeta42 (beta = 153.9, P = 0.041) in 1992 using age-adjusted linear regression. Compared with the lowest tertile of potassium, the middle (beta = 95.3, P = 0.138) and highest tertiles (beta = 193.5, P = 0.004) had incrementally increased cerebrospinal fluid Abeta42 levels. Associations remained after controlling for blood pressure and other factors, and were similar among the 17 women in 1974 with available serum potassium. Potassium in 1980 and 1992 was not associated with cerebrospinal fluid Abeta42. Findings suggest low serum potassium in mid life, but not late life, is associated with low cerebrospinal fluid Abeta42 levels in late life. It is possible potassium co-varies with another variable that is associated with cerebrospinal fluid Abeta42. Nonetheless, serum potassium is a modifiable risk factor and further examination of the potassium-dementia relationship is warranted.

Cerebrospinal fluid markers and change in MMSE score over an 8-year follow-up period - the population study of women in Gothenburg, Sweden

Between 2010 and 2050, Alzheimer's disease (AD) willreach epidemic proportions, highlighting the importance of identifying appropriate preclinical markers for prevention. Biomarkers present in cerebrospinal fluid (CSF) may be useful for predicting progression from preclinical to clinical AD. We investigated the longitudinal relationship between cerebrospinal fluid markers - amyloid beta-42 (Abeta-42), tau, growth-associated protein-43 (GAP-43), and the CSF-to-serum albumin ratio (albumin ratio) - in relationship to dementia occurrence and change in Mini-Mental State Examination (MMSE) score over an 8-year follow-up period in a population-based sample of women. The MMSE and lumbar puncture were performed in 1992 on a representative sample of 84 women without dementia born in 1908, 1914, 1918, and 1922 (aged 70–84 years) as part of the Population Study of Women (PSW) in Göteborg, Sweden. Cerebrospinal fluid was analyzed for Abeta-42, GAP-43, tau protein, and the albumin ratio. Women were followed for 8 years after lumbar puncture for dementia occurrence and a repeat MMSE. Correlation and regression analyses and ANOVA were used to relate CSF markers, dementia, age, and change in MMSE score between 1992 and 2000. Women who developed dementia after 1992 (n=6) had a lower Abeta-42 (p=0.061) level, and higher tau (p=0.000) and GAP-43 (p=0.023) levels at baseline compared to women who did not become demented. Women who became demented also experienced a greater decline in MMSE score (p=0.000) between 1992 and 2000. Among 51 women who never developed dementia and who participated in the MMSE in 1992 and 2000, decline in MMSE score (range=3 to -8 points) was correlated with decreases in Abeta-42 (r=0.359, p=0.010). Of those experiencing a decline of at least 2 points in MMSE (n=14), mean Abeta-42 levels were lower compared to those who experienced no decline (p=0.025). In a multivariate linear regression model including all CSF markers and predicting change in MMSE, Abeta-42 was the sole predictor (R2=0.173, p=0.026). CSF Abeta-42 is a useful marker of cognitive decline as measured using the MMSE among elderly women without dementia, and CSF markers are useful predictors of dementia when measured at least one year prior to dementia onset.

Amyloid β 38, 40, and 42 species in cerebrospinal fluid: More of the same?

Various C-terminally truncated amyloid beta peptides (Abeta) are linked to Alzheimer's disease (AD) pathogenesis. Cerebrospinal fluid (CSF) concentrations of Abeta38, Abeta40, and Abeta42 were measured by enzyme-linked immunosorbent assay in 30 patients with AD and 26 control subjects. CSF Abeta42 levels was decreased in patients with AD, whereas CSF Abeta38 and Abeta40 levels were similar in patients with AD and control subjects. All three Abeta peptides were interrelated, particularly CSF Abeta38 and Abeta40. Diagnostic accuracy of CSF Abeta42 concentrations was not improved by applying the ratios of CSF Abeta42 to Abeta38 or Abeta40.

The diagnostic value of tau protein, β-amyloid (1-42) and their ratio for the discrimination of alcohol-related cognitive disorders from Alzheimer's disease in the early stages

Chronic and heavy alcohol abuse or dependence may result in impaired cognition and dementia. The increased risk of Alzheimer's disease (AD) in older individuals interferes with the differential diagnosis, especially when dealing with elderly patients with a long history of alcohol abuse. The aim of the present study was to evaluate the diagnostic value of the putative cerebrospinal fluid (CSF) biomarkers tau, beta-amyloid 1-42 (Abeta42) and their ratio in differentiating alcohol related cognitive disorder (ARCD) from AD. Double-sandwich ELISA (Innotest htau antigen and beta-Amyloid (1-42), Innogenetics) were used to quantify the above markers in a total of 20 patients with ARCD, 33 AD patients with mild to moderate dementia and 50 mentally intact subjects. Tau protein successfully differentiated AD from normal ageing with 96% specificity and 93.9% sensitivity and from ARCD with 95% specificity, and 87.9% sensitivity. Abeta42 alone had a specificity of 88% and a sensitivity of 69.7% in differentiating AD from normal ageing, while the corresponding values for differentiating AD from ARCD were 80% and 84.8% respectively. The tau/Abeta42 ratio was better than tau alone for differentiating AD from normal ageing (specificity 94%, sensitivity 97%) and better than any of the candidate markers alone, for differentiating AD from ARCD (specificity 100%, sensitivity 97%). The combined use of CSF tau and Abeta42 may be a useful tool in the differential diagnosis of ARCD from AD, especially in the early stages, where diagnostic uncertainty is greater.

Variants of CYP46A1 may interact with age and APOE to influence CSF Abeta42 levels in Alzheimer's disease.

Recent studies have suggested that variants of CYP46A1, encoding cholesterol 24-hydroxylase (CYP46), confer risk for Alzheimer's disease (AD), a prospect substantiated by evidence of genetic association from several quantitative traits related to AD pathology, including cerebrospinal fluid (CSF) levels of the 42 amino-acid cleavage product of beta-amyloid (Abeta42) and the tau protein. In the present study, these claims have been explored by the genotyping of previously associated markers in CYP46A1 in three independent northern European case-control series encompassing 1323 individuals and including approximately 400 patients with measurements of CSF Abeta42 and phospho-tau protein levels. Tests of association in case-control models revealed limited evidence that CYP46A1 variants contributed to AD risk across these samples. However, models testing for potential effects upon CSF measures suggested a possible interaction of an intronic marker (rs754203) with age and APOE genotype. In stratified analyses, significant effects were evident that were restricted to elderly APOE epsilon4 carriers for both CSF Abeta42 ( P=0.0009) and phospho-tau ( P=0.046). Computational analyses indicate that the rs754203 marker probably does not impact the binding of regulatory factors, suggesting that other polymorphic sites underlie the observed associations. Our results provide an important independent replication of previous findings, supporting the existence of CYP46A1 sequence variants that contribute to variability in beta-amyloid metabolism.

Cerebrospinal fluid Ab40 and Ab42: natural course and clinical usefulness

Amyloid beta protein 40 (Abeta40) and 42 Abeta42, major components of senile plaque amyloids, are physiological peptides present in the brain, cerebrospinal fluid (CSF) and plasma. The levels of CSF Abeta40 and Abeta42(43) show a U-shaped natural course in normal aging. The increase of Abeta42(43) over 60 years of age is inhibited in Alzheimer's disease (AD). This specific alteration of CSF Abeta42(43) correlates with Abeta deposits in the AD brain providing a biological basis for a biomarker of AD. In the GTT2 study, assays of the CSF Abeta ratio ((Abeta40/ Abeta42(43)) showed a diagnostic sensitivity (59%) and specificity (88%) compared with non-AD type dementia and controls. The levels of the Abeta ratio increased from early to late stages of AD. Combination assays of CSF tau and Abeta ratio provided further efficient diagnostic sensitivity (81%) and specificity (87%). The reliability of the assay may prompt worldwide usage of these CSF biomarkers for Alzheimer's patients.

Cerebrospinal fluid Abeta40 and Abeta42: natural course and clinical usefulness.

Amyloid beta protein 40 (Abeta40) and 42 Abeta42, major components of senile plaque amyloids, are physiological peptides present in the brain, cerebrospinal fluid (CSF) and plasma. The levels of CSF Abeta40 and Abeta42(43) show a U-shaped natural course in normal aging. The increase of Abeta42(43) over 60 years of age is inhibited in Alzheimer's disease (AD). This specific alteration of CSF Abeta42(43) correlates with Abeta deposits in the AD brain providing a biological basis for a biomarker of AD. In the GTT2 study, assays of the CSF Abeta ratio ((Abeta40/ Abeta42(43)) showed a diagnostic sensitivity (59%) and specificity (88%) compared with non-AD type dementia and controls. The levels of the Abeta ratio increased from early to late stages of AD. Combination assays of CSF tau and Abeta ratio provided further efficient diagnostic sensitivity (81%) and specificity (87%). The reliability of the assay may prompt worldwide usage of these CSF biomarkers for Alzheimer's patients.

Cerebrospinal fluid Aβ40 and Aβ42: Natural course and clinical usefulness

Amyloid β protein 40 (Aβ40) and 42 (Aβ42), major components of senile plaque amyloids, are physiological peptides present in the brain, cerebrospinal fluid (CSF) and plasma. The levels of CSF Aβ40 and Aβ42(43) show a U-shaped natural course in normal aging. The increase of Aβ42(43) over 60 years of age is inhibited in Alzheimer's disease (AD). This specific alteration of CSF Aβ42(43) correlates with Aβ deposits in the AD brain providing a biological basis for a biomarker of AD. In the GTT2 study, assays of the CSF Aβ ratio [(Aβ40/ Aβ42(43)] showed a diagnostic sensitivity (59%) specificity (88%) The levels of the Aβ ratio increased from early to late stages of AD. Combination assays of CSF tau and Aβ ratio provided further efficient diagnostic sensitivity (81%) reliability of the assay may prompt worldwide usage of these CSF biomarkers for Alzheimer's patients.

The levels of cerebrospinal fluid Abeta40 and Abeta42(43) are regulated age-dependently.

Decreased levels of cerebrospinal fluid (CSF) Abeta42 is a diagnostic marker of Alzheimer's disease. To clarify the biological basis of this marker, the physiological alterations of CSF Abeta40 and Abeta42 by aging were studied. CSF samples from 92 normal subjects between 8 and 89 years old were measured using a specific ELISA for Abeta40 and Abeta42(43). High concentrations of Abeta40 and Abeta42(43) in the young group, under 29 years old, changed to be at low concentrations in the adult group between 30 and 59 years old. Subsequently, the levels increased again with age. Third order regression analysis showed a significant correlation between the levels of Abeta40 and age (Y = - 169 X(3) + 3.1X(2)- 0.02X + 4135; P < 0.034) and between the levels of Abeta42(43) and age (Y = - 46 X(3) + 0.9 X(2)- 0.005X + 992; P < 0.005). The levels of CSF Abeta40 and Abeta42(43) were physiologically regulated to show a U-shaped natural course in normal aging. These findings suggested that the physiological increase of Abeta42(43) over 59 years of age is selectively inhibited in Alzheimer's disease.

Prominent Cerebral Amyloid Angiopathy in Transgenic Mice Overexpressing the London Mutant of Human APP in Neurons

Deposition of amyloid beta-peptide (Abeta) in cerebral vessel walls (cerebral amyloid angiopathy, CAA) is very frequent in Alzheimer's disease and occurs also as a sporadic disorder. Here, we describe significant CAA in addition to amyloid plaques, in aging APP/Ld transgenic mice overexpressing the London mutant of human amyloid precursor protein (APP) exclusively in neurons. The number of amyloid-bearing vessels increased with age, from approximately 10 to >50 per coronal brain section in APP/Ld transgenic mice, aged 13 to 24 months. Vascular amyloid was preferentially deposited in arterioles and ranged from small focal to large circumferential depositions. Ultrastructural analysis allowed us to identify specific features contributing to weakening of the vessel wall and aneurysm formation, ie, disruption of the external elastic lamina, thinning of the internal elastic lamina, interruption of the smooth muscle layer, and loss of smooth muscle cells. Biochemically, the much lower Abeta42:Abeta40 ratio evident in vascular relative to plaque amyloid, demonstrated that in blood vessel walls Abeta40 was the more abundant amyloid peptide. The exclusive neuronal origin of transgenic APP, the high levels of Abeta in cerebrospinal fluid compared to plasma, and the specific neuroanatomical localization of vascular amyloid strongly suggest specific drainage pathways, rather than local production or blood uptake of Abeta as the primary mechanism underlying CAA. The demonstration in APP/Ld mice of rare vascular amyloid deposits that immunostained only for Abeta42, suggests that, similar to senile plaque formation, Abeta42 may be the first amyloid to be deposited in the vessel walls and that it entraps the more soluble Abeta40. Its ability to diffuse for larger distances along perivascular drainage pathways would also explain the abundance of Abeta40 in vascular amyloid. Consistent with this hypothesis, incorporation of mutant presenilin-1 in APP/Ld mice, which resulted in selectively higher levels of Abeta42, caused an increase in CAA and senile plaques. This mouse model will be useful in further elucidating the pathogenesis of CAA and Alzheimer's disease, and will allow testing of diagnostic and therapeutic strategies.

Quantification of Alzheimer Amyloid β Peptides Ending at Residues 40 and 42 by Novel ELISA Systems

The amyloid beta (Abeta) peptide is a key molecule in the pathogenesis of Alzheimer's disease. Reliable methods to detect and quantify soluble forms of this peptide in human biological fluids and in model systems, such as cell cultures and transgenic animals, are of great importance for further understanding the disease mechanisms. In this study, the application of new and highly specific ELISA systems for quantification of Abeta40 and Abeta42 (Abeta peptides ending at residues 40 or 42, respectively) in human cerebrospinal fluid (CSF) are presented. Monoclonal antibodies WO-2, G2-10 and G2-11 were thoroughly characterized by (SPOT) epitope mapping and immunoprecipitation/mass spectrometry. We determined whether aggregation affected the binding capacities of the antibodies to synthetic peptides and whether components of the CSF affected the ability of the antibodies to bind synthetic Abeta1-40 and Abeta1-42 peptides. The stability of Abeta40 and Abeta42 in CSF during different temperature conditions was also studied to optimize sample handling from lumbar puncture to Abeta assay. The detection range for the ELISAs were 20-250 pM. The intra-assay variations were 2% and 3%, and the inter-assay variations were 2% and 10% for Abeta40 and Abeta42, respectively. The antibodies specifically detected the expected peptides with equal affinity for soluble and fibrillar forms of the peptide. The presence of CSF obstructed the recognition of synthetic peptides by the antibodies and the immunoreactivity of endogenous CSF Abeta decreased with increasing storage time and temperature. This study describes highly sensitive ELISAs with thoroughly characterized antibodies for quantification of Abeta40 and Abeta42, an important tool for the understanding of the pathogenesis of Alzheimer's disease. Our results pinpoint some of the difficulties associated with Abeta quantification and emphasize the importance of using a well-documented assay.