Amyloid-beta Peptide Levels Research Articles

β‐amyloid peptides in cerebrospinal fluid of patients with Creutzfeldt–Jakob disease

Decreased levels of beta-amyloid peptide 1-42 (Abeta1-42) in cerebrospinal fluid (CSF) are a characteristic feature of Alzheimer's disease (AD) but recently were also observed in Creutzfeldt-Jakob disease (CJD). We analyzed the CSF of patients with CJD, and AD and nondemented controls using a quantitative urea-based Abeta sodium dodecyl sulfate polyacrylamide gel electrophoresis immunoblot. Like in AD and nondemented controls, we found a highly conserved pattern of carboxyterminally truncated Abeta1-37/38/39 in addition to Abeta1-40/42 also in CJD patients. By the introduction of the ratio Abeta1-39 to Abeta1-42, CJD and AD can effectively be differentiated. We conclude that the immunoblot shows disease-specific CSF Abeta peptide patterns in CJD and AD and suppose that measurement of the Abeta peptide pattern seems to be a promising diagnostic tool in the differential diagnosis of dementias.

Glucagon-like peptide-1 decreases endogenous amyloid-beta peptide (Abeta) levels and protects hippocampal neurons from death induced by Abeta and iron.

Glucagon-like peptide-1(7-36)-amide (GLP-1) is an endogenous insulinotropic peptide that is secreted from the gastrointestinal tract in response to food. It enhances pancreatic islet beta-cell proliferation and glucose-dependent insulin secretion and lowers blood glucose and food intake in patients with type 2 diabetes mellitus. GLP-1 receptors, which are coupled to the cyclic AMP second messenger pathway, are expressed throughout the brains of rodents and humans. It was recently reported that GLP-1 and exendin-4, a naturally occurring, more stable analogue of GLP-1 that binds at the GLP-1 receptor, possess neurotrophic properties and can protect neurons against glutamate-induced apoptosis. We report here that GLP-1 can reduce the levels of amyloid-beta peptide (Abeta) in the brain in vivo and can reduce levels of amyloid precursor protein (APP) in cultured neuronal cells. Moreover, GLP-1 and exendin-4 protect cultured hippocampal neurons against death induced by Abeta and iron, an oxidative insult. Collectively, these data suggest that GLP-1 can modify APP processing and protect against oxidative injury, two actions that suggest a novel therapeutic target for intervention in Alzheimer's disease.

Increased brain beta-amyloid load, phosphorylated tau, and risk of Alzheimer disease associated with an intronic CYP46 polymorphism.

CYP46, the gene encoding cholesterol 24-hydroxylase, plays a key role in the hydroxylation of cholesterol and thereby mediates its removal from brain. To study the association of polymorphic sites on CYP46 with Alzheimer disease (AD) traits and with the risk of the development of AD. Alzheimer disease traits (beta-amyloid load, beta-amyloid peptides, hyperphosphorylated tau protein) were assessed in brain tissues and in the cerebrospinal fluid of patients with AD and control subjects. Genetic associations were studied in 2 independent populations. Specialized centers for memory disorders in Switzerland, Greece, and Italy. Fifty-five brain tissues from nondemented elderly patients for the histopathological studies; 38 patients with AD and 25 control subjects for the cerebrospinal fluid studies; 201 patients with AD and 248 control subjects for the genetic association studies. A polymorphism of CYP46 was associated with increased beta-amyloid load in brain tissues as well as with increased cerebrospinal fluid levels of beta-amyloid peptides and phosphorylated tau protein. Moreover, this CYP46 polymorphism was associated with higher risk of late-onset sporadic AD in 2 independent populations (odds ratio, 2.16; 95% confidence interval [CI], 1.41-3.32; P<.001). The additional presence of 1 or 2 apolipoprotein E epsilon4 alleles synergistically increased the risk of AD to an odds ratio of 9.6 (95% CI, 4.9-18.9; P<.001) as compared with 4.4 for apolipoprotein E epsilon4 alone (95% CI, 2.8-6.8; P<.001). CYP46 influences brain beta-amyloid load, cerebrospinal fluid levels of beta-amyloid peptides and phosphorylated tau, and the genetic risk of late-onset sporadic AD.

Effects of chronic hypoxia on Ca(2+) stores and capacitative Ca(2+) entry in human neuroblastoma (SH-SY5Y) cells.

Microfluorimetric measurements of intracellular calcium ion concentration [Ca(2+)](i) were employed to examine the effects of chronic hypoxia (2.5% O(2), 24 h) on Ca(2+) stores and capacitative Ca(2+) entry in human neuroblastoma (SH-SY5Y) cells. Activation of muscarinic receptors evoked rises in [Ca(2+)](i) which were enhanced in chronically hypoxic cells. Transient rises of [Ca(2+)](i) evoked in Ca(2+)-free solutions were greater and decayed more slowly following exposure to chronic hypoxia. In control cells, these transient rises of [Ca(2+)](i) were also enhanced and slowed by removal of external Na(+), whereas the same manoeuvre did not affect responses in chronically hypoxic cells. Capacitative Ca(2+) entry, observed when re-applying Ca(2+) following depletion of intracellular stores, was suppressed in chronically hypoxic cells. Western blots revealed that presenilin-1 levels were unaffected by chronic hypoxia. Exposure of cells to amyloid beta peptide (1-40) also increased transient [Ca(2+)](i) rises, but did not mimic any other effects of chronic hypoxia. Our results indicate that chronic hypoxia causes increased filling of intracellular Ca(2+) stores, suppressed expression or activity of Na(+)/Ca(2+) exchange and reduced capacitative Ca(2+) entry. These effects are not attributable to increased amyloid beta peptide or presenilin-1 levels, but are likely to be important in adaptive cellular remodelling in response to prolonged hypoxic or ischemic episodes.

α-1-Antichymotrypsin Promotes β-Sheet Amyloid Plaque Deposition in a Transgenic Mouse Model of Alzheimer's Disease

Alpha(1)-antichymotrypsin (ACT), an acute-phase inflammatory protein, is an integral component of the amyloid deposits in Alzheimer's disease (AD) and has been shown to catalyze amyloid beta-peptide polymerization in vitro. We have investigated the impact of ACT on amyloid deposition in vivo by generating transgenic GFAP-ACT-expressing mice and crossing them with the PDGF-hAPP/V717F mice, which deposit amyloid in an age-dependent manner. The number of amyloid deposits measured by Congo Red birefringence was increased in the double ACT/amyloid precursor protein (APP) transgenic mice compared with transgenic mice that only expressed APP, particularly in the hippocampus where ACT expression was highest, and the increase was preceded by elevated total amyloid beta-peptide levels at an early age. Our data demonstrate that ACT promotes amyloid deposition and provide a specific mechanism by which inflammation and the subsequent upregulation of astrocytic ACT expression in AD brain contributes to AD pathogenesis.

Dysregulation of cellular calcium homeostasis in Alzheimer's disease: bad genes and bad habits.

Calcium is one of the most important intracellular messengers in the brain, being essential for neuronal development, synaptic transmission and plasticity, and the regulation of various metabolic pathways. The findings reviewed in the present article suggest that calcium also plays a prominent role in the pathogenesis of Alzheimer's disease (AD). Associations between the pathological hallmarks ofAD (neurofibrillary tangles [NFT] and amyloid plaques) and perturbed cellular calcium homeostasis have been established in studies of patients, and in animal and cell culture models of AD. Studies of the effects of mutations in the beta-amyloid precursor protein (APP) and presenilins on neuronal plasticity and survival have provided insight into the molecular cascades that result in synaptic dysfunction and neuronal degeneration in AD. Central to the neurodegenerative process is the inability of neurons to properly regulate intracellular calcium levels. Increased levels of amyloid beta-peptide (Abeta) induce oxidative stress, which impairs cellular ion homeostasis and energy metabolism and renders neurons vulnerable to apoptosis and excitotoxicity. Subtoxic levels of Abeta may induce synaptic dysfunction by impairing multiple signal transduction pathways. Presenilin mutations perturb calcium homeostasis in the endoplasmic reticulum in a way that sensitizes neurons to apoptosis and excitotoxicity; links between aberrant calcium regulation and altered APP processing are emerging. Environmental risk factors for AD are being identified and may include high calorie diets, folic acid insufficiency, and a low level of intellectual activity (bad habits); in each case, the environmental factor impacts on neuronal calcium homeostasis. Low calorie diets and intellectual activity may guard against AD by stimulating production of neurotrophic factors and chaperone proteins. The emerging picture of the cell and molecular biology of AD is revealing novel preventative and therapeutic strategies for eradicating this growing epidemic of the elderly.

Autoantibodies to amyloid-beta and Alzheimer's disease.

Immunization against amyloid-beta has been suggested as a possible preventive or therapeutic treatment for Alzheimer's disease. We hypothesized that some individuals may have autoantibodies to amyloid-beta and that this may be protective. We analyzed the plasma of 365 individuals, drawn from a larger longitudinal epidemiological study, for the presence of antibodies to amyloid-beta. There were detectable but very low levels of anti-amyloid-beta antibodies in just over 50% of all samples and modest levels in under 5% of all samples. However, neither the presence nor the level of anti-amyloid-beta antibodies correlated with the likelihood of developing dementia or with plasma levels of amyloid-beta peptide. These data suggest that low levels of anti-amyloid-beta autoantibodies are frequent in the elderly population but do not confer protection against developing dementia.

Correlation between elevated levels of amyloid beta-peptide in the brain and cognitive decline.

Alzheimer disease (AD) is characterized neuropathologically by the presence of amyloid beta-peptide (Abeta)-containing plaques and neurofibrillary tangles composed of abnormal tau protein. Considerable controversy exists as to whether the extent of accumulation of Abeta correlates with dementia and whether Abeta alterations precede or follow changes in tau. To determine whether accumulation of Abeta correlates with the earliest signs of cognitive deterioration and to define the relationship between Abeta accumulation and early tau changes. Postmortem cross-sectional study of 79 nursing home residents with Clinical Dementia Rating (CDR) scale scores of 0.0 to 5.0 who died between 1986 and 1997, comparing the levels of Abeta variants in the cortices of the subjects with no (CDR score, 0.0 [n = 16]), questionable (CDR score, 0.5 [n = 11]), mild (CDR score, 1.0 [n = 22]), moderate (CDR score, 2.0 [n = 15]), or severe (CDR score, 4.0 or 5.0 [n = 15]) dementia. Levels of total Abeta peptides with intact or truncated amino termini and ending in either amino acid 40 (A(beta)x-40) or 42 (A(beta)x-42) in 5 neocortical brain regions as well as levels of tau protein undergoing early conformational changes in frontal cortex, as a function of CDR score. The levels of both A(beta)x-40 and A(beta)x-42 were elevated even in cases classified as having questionable dementia (CDR score = 0.5), and increases of both peptides correlated with progression of dementia. Levels of the more fibril-prone A(beta)x-42 peptide were higher than those of A(beta)x-40 in nondemented cases and remained higher throughout progression of disease in all regions examined. Finally, increases in A(beta)x-40 and A(beta)x-42 precede significant tau pathology at least in the frontal cortex, an area chosen for examination because of the absence of neuritic changes in the absence of disease. In this study, levels of total A(beta)x-40 and A(beta)x-42 were elevated early in dementia and levels of both peptides were strongly correlated with cognitive decline. Of particular interest, in the frontal cortex, Abeta was elevated before the occurrence of significant tau pathology. These results support an important role for Abeta in mediating initial pathogenic events in AD dementia and suggest that treatment strategies targeting the formation, accumulation, or cytotoxic effects of Abeta should be pursued.

Enhancer function and novel DNA binding protein activity in the near upstream betaAPP gene promoter.

The role of betaAPP gene transcription and promoter regulation in modifying amyloid beta-peptide (Abeta) levels is not well understood. Increased production of Abeta or changes in Abeta42/Abeta40 ratio by fibroblasts occurs in the presence of mutant presenilin or betaAPP alleles in familial Alzheimer's disease subjects. Both betaAPP mRNA and Abeta levels are increased in trisomy 21. The APP gene promoter is in a class of housekeeping genes and contains two putative consensus sites for the binding of transcription factor AP1. Electrophoretic mobility shift (EMSA) and DNase protection assays using human fibroblast and HeLa nuclear extract identified specific protein binding with novel Sp1-like properties to both a near-upstream and a downstream domain of the betaAPP promoter. The upstream binding activity was localized to a putative AP1 consensus site and its immediate 5'-adjacent GC-rich element. However, c-Jun antibody and competition experiments had no effect on binding to this domain. A series of 5'-deleted betaAPP promoter-reporter gene transfections in HeLa and fibroblast cells showed that the domain-containing region, n.t. -383 to -348, exerts a 2.9-fold activating influence on basal pbetaAPP-reporter transcription. When subcloned to test enhancer function, the 5'-GC element/'AP1 site' tandem construct conferred four-fold greater activity than either element alone and two-fold greater than the more 3'-situated HSE consensus sequence. Phorbol ester treatment had no effect in these reporter assays. This element shares homology and binding properties with a domain immediately 5' to the downstream E-box/USF element. An interaction model involving both domains and looping of interjacent DNA is proposed. We conclude that this newly described binding protein-enhancer complex is required for full betaAPP promoter activation.

Are children with down syndrom under the oxidative stress?

We examined the contribution of candidates genes for Alzheimer's disease (AD) to individual differences in levels of beta amyloid peptides in adults with Down syndrom, a population at high risk for AD. Participants were 254 non-demented adults with Down syndrome, 30–78 years of age. Genomic deoxyribonucleic acid was genotyped using an Illumina GoldenGate custom array. We used linear regression to examine differences in levels of Aβ peptides associated with the number of risk alleles, adjusting for age, sex, level of intellectual disability, race and/or ethnicity, and the presence of the APOE ε4 allele. For Aβ42 levels, the strongest gene-wise association was found for a single nucleotide polymorphism (SNP) on CAHLM1; for Aβ40 levels, the strongest gene-wise associations were found for SNPs in IDE and SOD1, while the strongest gene-wise associations with levels of the Aβ42/Aβ40 ratio were found for SNPs in SORCS1. Broadly classified, variants in these genes may influence amyloid precursor protein processing (CALHM1, IDE), vesicular trafficking (SORCS1), and response to oxidative stress (SOD1).

Cerebrospinal fluid levels of alpha-secretase-cleaved soluble amyloid precursor protein mirror cognition in a Swedish family with Alzheimer disease and a gene mutation.

To explore the relationship between possible biological markers of Alzheimer disease that are related to amyloid metabolism and mental functions. Twelve individuals from a Swedish family with Alzheimer disease and a double mutation at codons 670/671 of the amyloid precursor protein gene participated in the study. Cerebrospinal fluid levels of alpha-secretase cleaved soluble amyloid precursor protein (alpha-sAPP), total sAPP, and amyloid beta-peptide were correlated with data on multiple cognitive functions that covered the whole range of human performance. The Alzheimer's Disease Research Centre, Department of Clinical Neuroscience, Section of Geriatric Medicine, Karolinska Institute, Huddinge University Hospital, Huddinge, Sweden. There were highly significant linear correlations between low levels of alpha-sAPP and poor performance on neuropsychological tests that assessed intelligence, verbal and visuospatial functions, memory, and attention. Within the group of nonmutation carriers, significant correlations were also obtained between the levels of alpha-sAPP and cognitive functions. A less striking association was seen between the levels of total sAPP and cognition. No association was found between the levels of amyloid beta-peptide and cognition. The strong relationship between alpha-sAPP levels and cognition in both patients with Alzheimer disease and normal-aging persons may imply that alpha-sAPP is involved in basic protective brain processes. Alternatively, less amyloid beta-peptide amounts are produced, leading to diminished plaque formation, when alpha-sAPP is generated.

The E280A presenilin 1 Alzheimer mutation produces increased A beta 42 deposition and severe cerebellar pathology.

Missense mutations in the presenilin 1 (PS1) gene cause the most common form of dominant early-onset familial Alzheimer's disease (FAD) and are associated with increased levels of amyloid beta-peptides (A beta) ending at residue 42 (A beta 42) in plasma and skin fibroblast media of gene carriers. A beta 42 aggregates readily and appears to provide a nidus for the subsequent aggregation of A beta 40 (ref. 4), resulting in the formation of innumerable neuritic plaques. To obtain in vivo information about how PS1 mutations cause AD pathology at such early ages, we characterized the neuropathological phenotype of four PS1-FAD patients from a large Colombian kindred bearing the codon 280 Glu to Ala substitution (Glu280Ala) PS1 mutation. Using antibodies specific to the alternative carboxy-termini of A beta, we detected massive deposition of A beta 42, the earliest and predominant form of plaque A beta to occur in AD (ref. 6-8), in many brain regions. Computer-assisted quantification revealed a significant increase in A beta 42, but not A beta 40, burden in the brains from 4 PS1-FAD patients compared with those from 12 sporadic AD patients. Severe cerebellar pathology included numerous A beta 42-reactive plaques, many bearing dystrophic neurites and reactive glia. Our results in brain tissue are consistent with recent biochemical evidence of increased A beta 42 levels in PS1-FAD patients and strongly suggest that mutant PS1 proteins alter the proteolytic processing of the beta-amyloid precursor protein at the C-terminus of A beta to favor deposition of A beta 42.