Amyloid-Beta (Aβ)

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Amyloid-Beta (Aβ)

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Amyloid-Beta (Aβ)

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Amyloid-beta (Aβ)</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[APP](/genes/app)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P05067" target="_blank">P05067</a></td>
</tr>
<tr>
<td class="label">PDB</td>
<td><a href="https://www.rcsb.org/structure/1IYT" target="_blank">1IYT</a>, <a href="https://www.rcsb.org/structure/1BA4" target="_blank">1BA4</a>, <a href="https://www.rcsb.org/structure/2BEG" target="_blank">2BEG</a>, <a href="https://www.rcsb.org/structure/5OQV" target="_blank">5OQV</a></td>
</tr>
<tr>
<td class="label">Mol.

...

Amyloid-Beta (Aβ)

<table class="infobox infobox-protein">
<tr>
<th class="infobox-header" colspan="2">Amyloid-beta (Aβ)</th>
</tr>
<tr>
<td class="label">Gene</td>
<td>[APP](/genes/app)</td>
</tr>
<tr>
<td class="label">UniProt</td>
<td><a href="https://www.uniprot.org/uniprot/P05067" target="_blank">P05067</a></td>
</tr>
<tr>
<td class="label">PDB</td>
<td><a href="https://www.rcsb.org/structure/1IYT" target="_blank">1IYT</a>, <a href="https://www.rcsb.org/structure/1BA4" target="_blank">1BA4</a>, <a href="https://www.rcsb.org/structure/2BEG" target="_blank">2BEG</a>, <a href="https://www.rcsb.org/structure/5OQV" target="_blank">5OQV</a></td>
</tr>
<tr>
<td class="label">Mol. Weight</td>
<td>4 kDa (Aβ40/42)</td>
</tr>
<tr>
<td class="label">Localization</td>
<td>Extracellular, membrane-associated</td>
</tr>
<tr>
<td class="label">Family</td>
<td>[Amyloid precursor protein](/entities/app-protein) family</td>
</tr>
<tr>
<td class="label">Diseases</td>
<td>[Alzheimer's Disease](/diseases/alzheimers), [Cerebral Amyloid Angiopathy](/diseases/cerebral-amyloid-angiopathy)</td>
</tr>
<tr>
<td class="label">Associated Diseases</td>
<td><a href="/wiki/als" style="color:#ef9a9a">ALS</a>, <a href="/wiki/alzheimer" style="color:#ef9a9a">ALZHEIMER</a>, <a href="/wiki/alzheimer-disease" style="color:#ef9a9a">ALZHEIMER DISEASE</a>, <a href="/wiki/alzheimer's" style="color:#ef9a9a">ALZHEIMER'S</a>, <a href="/wiki/alzheimer's-disease" style="color:#ef9a9a">ALZHEIMER'S DISEASE</a></td>
</tr>
<tr>
<td class="label">KG Connections</td>
<td><a href="/atlas" style="color:#4fc3f7">3014 edges</a></td>
</tr>
</table>

Amyloid-beta (Aβ)

Overview

Amyloid-beta (Aβ) is a peptide fragment derived from the proteolytic processing of the [Amyloid Precursor Protein (APP)](/amyloid-precursor-protein-(app)))))))), encoded by the [APP](/entities/app-protein) gene on chromosome 21. It is a 40-42 amino acid peptide that plays a central role in the pathogenesis of Alzheimer's disease (AD) and related amyloidopathies[@hardy2002].

Amyloidogenic Processing

APP Processing Pathway

Mermaid diagram (expand to render)

APP can be processed through two mutually exclusive pathways:

Non-amyloidogenic pathway: alpha-secretase cleaves APP within the Abeta sequence, precluding Abeta formation. This pathway produces soluble APPalpha (sAPPalpha) and a membrane-bound C-terminal fragment.

Amyloidogenic pathway: beta-secretase (BACE1) cleaves APP at the N-terminus of Abeta, followed by gamma-secretase cleavage at the C-terminus, releasing Abeta peptides of various lengths (Abeta38, Abeta40, Abeta42, Abeta43)[@obrien2011].

The Abeta42 isoform is more hydrophobic and aggregation-prone than Abeta40, making it the primary species found in amyloid plaques.

See also: [APP Amyloid Pathway](/mechanisms/app-amyloid-pathway-alzheimers).

Molecular Structure

Primary Sequence and Domains

Amyloid-beta peptides are derived from the transmembrane domain of [APP](/entities/app-protein), with the Aβ sequence spanning residues 681-770 of the APP770 isoform. The peptide contains:

N-terminal region (1-16): Highly hydrophilic, forms the "soft" segment that initiates aggregation
Central hydrophobic core (17-21, KLVFF): Critical for fibril formation, known as the "KLVFF" motif
C-terminal region (22-40/42): Hydrophobic, drives membrane association and aggregation

Secondary and Tertiary Structure

In solution, monomeric Aβ adopts a random coil conformation. Upon aggregation, it transitions to:

β-sheet structure: Cross-β architecture with strands perpendicular to the fibril axis
Hydrophobic interactions: Drive the formation of the steric zipper
Salt bridges: Stabilize the fibril core (e.g., D23-K28 ionic interaction)

Cryo-EM studies have revealed multiple Aβ42 fibril morphologies:

3-fold symmetric protofilaments (common in sporadic AD)
2-fold symmetric dimers (familial AD cases)
Polymorphic strains: Different conformations associated with distinct disease phenotypes

Available PDB structures include: [1IYT](https://www.rcsb.org/structure/1IYT), [1BA4](https://www.rcsb.org/structure/1BA4), [2BEG](https://www.rcsb.org/structure/2BEG), [5OQV](https://www.rcsb.org/structure/5OQV), [7JTL](https://www.rcsb.org/structure/7JTL), [7JYY](https://www.rcsb.org/structure/7JYY).

The protein's three-dimensional structure can also be explored via the [AlphaFold Protein Structure Database](https://alphafold.ebi.ac.uk/entry/P05067).

Post-Translational Modifications

Aβ undergoes numerous PTMs that modulate its aggregation and toxicity:

Phosphorylation

Ser8: phosphorylation reduces aggregation
Ser26: affects membrane interactions
Tyrosine10: nitration enhances toxicity

Truncation

N-terminally truncated species (AβpE3, AβpE11): More aggregation-prone, found in plaques
C-terminally truncated species (Aβ1-38): Less toxic, may be protective

Isomerization

Asp7 isomerization: Affects aggregation kinetics
Asp23 isomerization: Alters fibril structure

Oxidation

Methionine35 oxidation: Reduces aggregation but increases toxicity of oligomers
Histidine oxidation: Modifies metal binding

Glycation

Advanced glycation end products (AGEs): Cross-link Aβ, enhance aggregation
Found in AD brain: Correlates with disease severity

Aggregation and Toxicity

Nucleation-Dependent Polymerization

Aβ aggregation follows a nucleation-dependent polymerization mechanism (also called "seeded growth"):

Lag phase: Monomers slowly form unstable oligomers

Nucleation: Critical nucleus forms (typically 2-6 monomers)

Elongation: Rapid addition of monomers to seed

Saturation: Equilibrium between monomers and fibrils

Mermaid diagram (expand to render)

Aggregation Prone Regions

The central hydrophobic core (CHC, residues 17-21, KLVFF) is critical for:

Steric zipper formation: Intermolecular β-sheet stacking
Oligomerization: Dimer/trimer formation
Fibril elongation: Monomer addition to fibril ends

The C-terminal hydrophobic tail (residues 30-42) drives:

Membrane association: Hydrophobic interactions with lipid bilayers
Fibril stability: Inter-protomer hydrogen bonds

Soluble Oligomers: The Toxic Species

Soluble Aβ oligomers (also called Aβ-derived diffusible ligands, ADDLs) are now recognized as the most toxic species, more so than mature fibrils or plaques[@lacor2008]. Key oligomer species include:

Dimers: Smallest toxic unit, ~9 kDa
Trimers: ~13.5 kDa, highly synaptotoxic
Tetramers: ~18 kDa, may be "off-pathway"
Dodecamers (Aβ*56): ~56 kDa, disrupts memory in mice
Large oligomers: >100 kDa, membrane-permeable

Membrane-Mediated Effects

Aβ interacts with multiple membrane components:

Lipid rafts: Aβ accumulates in cholesterol-rich microdomains

Ion channels: Forms Ca²⁺-permeable pores

Receptors: Binds to NMDA, AMPA, insulin receptors

Membrane fluidity: Alters lipid organization

Synaptic vesicle: Impairs neurotransmitter release

Mechanisms of Neurotoxicity

Aβ exerts toxicity through multiple interconnected mechanisms:

Synaptic dysfunction: Aβ oligomers bind to synaptic receptors (PrPᶜ, NMDA, mGluR5), impairing [long-term potentiation](/mechanisms/long-term-potentiation) (LTP), reducing dendritic spine density, and disrupting neurotransmitter release[@shankar2008]

Oxidative stress: Aβ accumulation increases [reactive oxygen species](/entities/reactive-oxygen-species) (ROS) production through:

Mitochondrial complex III dysfunction
NADPH oxidase activation
Metal redox cycling (Fe²⁺/Cu⁺ oxidation)
Lipid peroxidation

Neuroinflammation: Aβ activates [microglia](/cell-types/microglia) and [astrocytes](/cell-types/astrocytes) through:

TLR2/4 pattern recognition receptor activation
[NLRP3 inflammasome](/mechanisms/nlrp3-inflammasome) activation
Cytokine/chemokine release (IL-1β, TNF-α, IL-6)
Chronic inflammation contributes to neurodegeneration

Calcium dysregulation: Aβ forms calcium-permeable channels in membranes:

Uncontrolled Ca²⁺ influx
Mitochondrial calcium overload
Calpain activation
[Apoptosis](/mechanisms/apoptosis) signaling

Mitochondrial dysfunction: Aβ localizes to mitochondria:

Impairs complex IV activity
Reduces ATP production
Increases ROS
Triggers mitophagy deficits

Endoplasmic reticulum stress: Aβ disrupts protein folding:

[UPR](/entities/unfolded-protein-response) activation
CHOP-mediated apoptosis
Calcium store depletion

[Autophagy](/entities/autophagy) impairment: Aβ disrupts autophagic flux:

mTORC1 hyperactivation
Lysosomal dysfunction
Autophagosome accumulation

See also: [Amyloid Aggregation](/mechanisms/amyloid-aggregation), [Amyloid Hypothesis](/mechanisms/amyloid-hypothesis), and [Amyloid-Tau Synergistic Interaction](/mechanisms/amyloid-tau-synergistic-interaction-hypothesis).

APP Processing and Genetic Risk

Amyloid precursor protein (APP) processing determines Aβ production:

Non-Amyloidogenic Pathway (Protective)

The non-amyloidogenic pathway is the default processing route in healthy brains:

α-secretase cleavage: ADAM10/ADAM17 cleave APP at residue 16 (within the Aβ sequence)
sAPPα release: Produces soluble APPα, which has neuroprotective properties
CTFα formation: Creates a membrane-bound C-terminal fragment
[γ-secretase](/entities/gamma-secretase) processing: CTFα is further processed to p3 peptide (non-amyloidogenic)

The sAPPα fragment:

Promotes neurite outgrowth
Enhances synaptic plasticity
Has anti-inflammatory properties
Protects against excitotoxicity

Amyloidogenic Pathway (Pathogenic)

The amyloidogenic pathway generates Aβ peptides:

[β-secretase](/entities/bace1) (BACE1) cleavage: First cleavage at residue 1 of Aβ (APP residue 681)
sAPPβ release: Soluble APPβ fragment
CTFβ formation: C-terminal membrane fragment
γ-secretase cleavage: Multiple cleavage sites produce Aβ38-43

γ-secretase cleavage sites:

ε-site: Releases Aβ46-49 (longer fragments)
γ-site: Produces Aβ38-43 isoforms
ζ-site: Alternative cleavage

Genetic Risk Factors

APP Mutations (Autosomal Dominant)

| Mutation | Effect | Phenotype |
|----------|--------|-----------|
| Swedish (K670N/M671L) | ↑ Aβ production | Early-onset AD |
| Arctic (E22G) | ↑ Oligomerization | Aggressive AD |
| London (V717I) | ↑ Aβ42/Aβ40 | Early-onset AD |
| Flemish (A692G) | ↑ Aβ40 | CAA + AD |
| Dutch (E693Q) | ↑ Aβ aggregation | Severe CAA |
| Italian (E693K) | ↑ Aggregation | CAA |
| Iowa (D694N) | ↑ Aggregation | CAA + AD |

Protective APP Variants

A673V (Icelandic): Reduces Aβ production by 40%, carriers have 5x lower AD risk[@patterson2023]
A673T: Protective in vitro

APP copy number variants:

Duplication syndrome: APP triplication causes early-onset AD with CAA
Down syndrome: Extra APP copy leads to early Aβ accumulation

Genetic Risk Modifiers

BIN1: Affects Aβ trafficking and aggregation
PICALM: Modulates endocytosis and Aβ production
CLU (Clusterin): Aβ chaperone, genetic risk factor
ABCA7: Aβ clearance, lipid metabolism

Aβ Clearance Mechanisms

The brain has multiple pathways for Aβ clearance:

Proteolytic Degradation

Endogenous Aβ-degrading enzymes:

[Neprilysin](/entities/neprilysin) (NEP): Primary Aβ-degrading enzyme in brain
Expression decreases with age
NEP overexpression reduces plaques in mice
AAV-mediated NEP delivery in clinical trials
[Insulin-degrading enzyme](/entities/insulin-degrading-enzyme) (IDE): Aβ and insulin degradation
Located in cytoplasm, mitochondria, and extracellular space
Genetic variants affect AD risk
Matrix metalloproteinases (MMPs): MMP-2, MMP-9 degrade Aβ
Activated in glia
Increased in AD brain
Plasmin: Broad-spectrum protease
Activated by tPA
Lower in AD CSF
Cathepsins: Lysosomal proteases
Cathepsin B: Inhibited by cystatin C
Cathepsin D: Active in lysosomes

Microglial Clearance

Microglia clear Aβ through:

Receptor-mediated phagocytosis

TLRs (Toll-like receptors)
[RAGE](/genes/rage) (Receptor for Advanced Glycation Endproducts)
SR-A (Scavenger Receptor A)
CD36 (class B scavenger receptor)

Autophagy-lysosomal degradation

LC3-associated phagocytosis (LAP)
PICALM involvement
Damaged lysosomes impair clearance

Aβ export across the [blood-brain barrier](/entities/blood-brain-barrier)

[LRP1](/genes/lrp1) (Low-density lipoprotein receptor-related protein 1)
P-glycoprotein (ABCB1)
Age-related export decline

Peripheral Clearance

Peripheral Aβ affects brain Aβ through the "peripheral sink" hypothesis:

Liver and kidney clearance: Circulating Aβ degradation
Monocyte/macrophage uptake: Phagocytic clearance
Antibody-mediated clearance: Immunotherapy mechanisms
LDL receptor family: Aβ binding and clearance

Sleep and Glymphatic Clearance

The [glymphatic system](/entities/glymphatic-system) is critical for Aβ clearance:

Astrocytic AQP4 channels: Water flux
Arterial pulsation: Driving force
Sleep-dependent clearance: 60% more clearance during sleep
Aβ diurnal variation: Higher during wakefulness
Sleep disruption: Increases Aβ accumulation

Cellular and Animal Models

In Vitro Models

Cell lines: CHO, HEK293, N2a for APP processing
Primary [neurons](/entities/neurons): Mouse, rat, human
iPSC-derived neurons: Patient-specific models
3D neuronal cultures: Cerebral organoids
Blood-brain barrier models: Transwell systems

In Vivo Models

Transgenic Mouse Models

| Model | Mutation | Aβ Profile | Plaques | Notes |
|-------|----------|------------|---------|-------|
| APP/PS1 | APP Swe + PS1ΔE9 | Aβ40↑, Aβ42↑ | Yes | Common model |
| 5xFAD | 3 APP + 2 PS1 | Aβ42↑↑ | Yes | Aggressive |
| APP23 | APP Swe | Aβ40↑ | Yes | Swiss colony |
| Tg2576 | APP Swe | Aβ40↑ | Yes | Memory deficits |
| J20 | APP Indiana + Swedish | Aβ42↑ | Yes | Synaptic loss |
| 3xTG | APP + [tau](/proteins/tau) + PS1 | Aβ40/42 + [tau](/proteins/tau) | Yes | AD-like |

Key Findings from Models

Aβ oligomers cause synaptic dysfunction before plaques
Microglial activation precedes plaque formation
[Tau](/proteins/tau) pathology is required for full neurodegeneration
Aβ vaccination reduces plaques but not always cognitive decline

Non-Murine Models

C. elegans: Simplest model for aggregation studies
Drosophila: Express Aβ in fly brain
Zebrafish: Transparent model for development
NHPs (non-human primates): Closest to human physiology

Clinical Trials and Therapeutic Challenges

Aβ-targeting therapies have faced challenges:

Completed trials (unsuccessful):

Passive immunization (bapineuzumab, solanezumab)
Active immunization (AN1792)
γ-secretase inhibitors
BACE1 inhibitors

Lessons learned:

Early intervention may be critical
Biomarker selection matters
Target engagement necessary
Combination approaches needed

Ongoing strategies:

Anti-oligomer antibodies
Small molecule aggregation inhibitors
Vaccine approaches with improved design
Aβ clearance enhancement

See also: [Anti-Amyloid Therapeutics](/mechanisms/anti-amyloid-therapeutics).

Role in Disease

Amyloid-beta (Aβ) is implicated in the following neurodegenerative conditions:

[Alzheimer's Disease](/diseases/alzheimers-disease) - the predominant component of amyloid plaques
[Cerebral Amyloid Angiopathy](/diseases/cerebral-amyloid-angiopathy) - vascular amyloid deposits
Down syndrome - triplication of APP gene leads to early Aβ accumulation
[Dutch hereditary cerebral amyloid angiopathy](/diseases/cerebral-amyloid-angiopathy) - APP mutation causes severe CAA
[Arctic mutation](/diseases/arctic-alzheimers) - Aβ point mutation (E22G) causes aggressive Aβ aggregation

Amyloid Cascade Hypothesis

The amyloid cascade hypothesis, proposed by Hardy and Higgins in 1992, remains the dominant framework for understanding AD pathogenesis[@selkoe2016]:

Aβ accumulation precedes tau pathology

Aβ triggers downstream tau hyperphosphorylation

Neurofibrillary tangles form

Neuronal loss and cognitive decline follow

Despite clinical trial failures, the hypothesis has evolved:

Modified view: Aβ triggers, but tau drives neurodegeneration
Oligomer-centric: Soluble oligomers, not plaques, are toxic
Temporal model: Aβ effects are age-dependent and cumulative

Misfolding, aggregation, or dysfunction of Amyloid-beta (Aβ) contributes to neuronal damage through various mechanisms including proteotoxic stress, disrupted cellular signaling, and neuroinflammation.

Aβ in Down Syndrome (Trisomy 21)

Individuals with Down syndrome develop AD-like pathology by age 40-50:

APP triplication: Chromosome 21 carries extra APP copy
Aβ overexpression: 1.5x normal Aβ production
Early plaques: Aβ plaques appear in 20s-30s
Dementia risk: 50-70% develop dementia by age 60+

See also: [Down Syndrome Alzheimer's Disease](/mechanisms/down-syndrome-alzheimers).

Therapeutic Targeting

Amyloid-beta (Aβ) represents an important therapeutic target. Multiple drug development programs are exploring strategies to:

1. Reduce Production

BACE1 Inhibitors

Verubecestat (MK-8931): Failed in Phase 3 — too much target engagement caused cognitive worsening
Atabecestat: Failed due to liver toxicity
Challenge: BACE1 processes many other substrates critical for synaptic function

γ-Secretase Modulators (GSMs)

Notch-sparing modulators: Reduce Aβ42 production without Notch inhibition
Chronic use potential: More tolerable than inhibitors
Natural compounds: Some NSAIDs act as GSMs

2. Enhance Clearance

Passive Immunization

[Lecanemab](/entities/lecanemab) (Leqembi): FDA-approved, binds Aβ protofibrils, 27% slowing of cognitive decline[@van2023]
[Donanemab](/entities/donanemab) (Kisunla): FDA-approved, targets pyroglutamate-modified Aβ
Gantenerumab: Failed in Phase 3 (Gradear)
Aduhelm (aducanumab): Controversial FDA approval, withdrawn from market

Active Immunization

ACI-35 (Lipidated tau): Phase 2 — anti-phospho-tau vaccine
ABvac40: Phase 2 — targets Aβ40
CAD106: Phase 2/3 — targets Aβ1-6

3. Inhibit Aggregation

Small Molecule Inhibitors

Curcumin: Natural polyphenol, binds Aβ, anti-inflammatory
Epigallocatechin gallate (EGCG): Green tea catechin, disrupts oligomers
Broussoflavonol: Natural compound in paper mulberry
Anle138b: Triple aromatic compound, blocks oligomer formation[@wagner2019]

Metal Chelators

Clioquinol: Cu/Zn chelator, reduces Aβ toxicity
PBT2: Second-generation chelator, failed in Phase 2

4. Target Downstream Effects

Anti-inflammatory: Anti-TNFα, NSAIDs (failed in prevention trials)
Neuroprotective: AMPA modulators, neurotrophic factors
Synaptic restoration: BDNF analogs, M1 agonists
Metabolic support: GLP-1 agonists, metabolic enhancers

5. Emerging Approaches

Anti-Aβ Oligomer Antibodies

ACI-302: Preferentially targets toxic oligomers
BACI: Bispecific antibody approach

Aβ Degradation Enhancers

Neprilysin enhancement: Endogenous Aβ-degrading enzyme
IDE (insulin-degrading enzyme): Aβ clearance
Matrix metalloproteinases (MMPs): Aβ degradation

Peripheral Sink Strategies

Anti-peripheral Aβ antibodies: "Peripheral sink" hypothesis
Albumin-based approaches: Bind plasma Aβ, shift equilibrium

See also: [Anti-Amyloid Therapeutics](/mechanisms/anti-amyloid-therapeutics), [Amyloid-Beta 40 Biomarker](/biomarkers/amyloid-beta-40-abeta-40), [Amyloid-Beta 42/40 Ratio](/biomarkers/amyloid-beta-42-40-ratio).

Key Publications

[The amyloid hypothesis of Alzheimer's disease: progress and problems on the road to therapeutics](https://doi.org/10.1126/science.1072994). Science, 2002.

[Amyloid-beta peptide — a chemist's perspective](https://doi.org/10.1002/anie.200802474). Angew Chem Int Ed, 2009.

[Soluble oligomers of the amyloid beta-protein impair synaptic plasticity and behavior](https://doi.org/10.1093/brain/awn130). Brain, 2008.

[Lecanemab in Early Alzheimer's Disease](https://doi.org/10.1056/NEJMoa2212948). NEJM, 2022.

External Links

UniProt: [https://www.uniprot.org/uniprot/P05067](https://www.uniprot.org/uniprot/P05067)
AlphaFold: [Amyloid-beta (Aβ)](https://alphafold.ebi.ac.uk/entry/P05067)
PDB: [1IYT](https://www.rcsb.org/structure/1IYT), [1BA4](https://www.rcsb.org/structure/1BA4), [2BEG](https://www.rcsb.org/structure/2BEG), [5OQV](https://www.rcsb.org/structure/5OQV)

Brain Atlas Resources

Allen Human Brain Atlas: [Expression data for APP](https://human.brain-map.org/microarray/search/show?search_term=APP)
Allen Brain Atlas API: [Gene expression via BrainAtlas API](https://api.brain-map.org/api/v0/data/gene/APP/)
BrainSpan Atlas: [Developmental expression of APP](https://www.brainspan.org/)

Aβ Peptide Variants

Multiple Aβ peptide species exist due to alternative γ-secretase cleavage:

Major Species

| Species | Length | Abundance | Aggregation |
|---------|--------|----------|-------------|
| Aβ37 | 37 aa | Low | Low |
| Aβ38 | 38 aa | ~10% | Low |
| Aβ40 | 40 aa | ~80-90% | Moderate |
| Aβ42 | 42 aa | ~5-10% | High |
| Aβ43 | 43 aa | Trace | Very high |

Aβ42/Aβ40 Ratio

Elevated Aβ42/Aβ40 ratio increases aggregation risk
APP mutations can shift production toward Aβ42
The ratio is a biomarker for AD risk

truncAβ Species

N-terminally truncated Aβ (pE3-Aβ42, pE11-Aβ42)
More aggregation-prone
Found in early-onset AD and CAA

Aβ Biomarkers

Cerebrospinal Fluid (CSF) Biomarkers

| Biomarker | Change in AD | Clinical Utility |
|-----------|--------------|------------------|
| Aβ40 | Decreased | Reflects global Aβ production |
| Aβ42 | Decreased | Reflects plaque deposition |
| Aβ42/Aβ40 ratio | Decreased | Improved diagnostic accuracy |
| Total tau (t-tau) | Increased | Neurodegeneration marker |
| Phospho-tau (p-tau) | Increased | Tau pathology marker |

Blood-Based Biomarkers

Aβ42/Aβ40 ratio: Plasma ratio shows promise for screening
p-tau181, p-tau217, p-tau231: Phospho-tau isoforms correlate with Aβ burden
[Neurofilament light](/biomarkers/neurofilament-light-chain-nfl) (NfL): Axonal damage marker
[GFAP](/entities/gfap): Astrocyte activation marker

Imaging Biomarkers

Amyloid PET (PiB, Florbetapir, Florbetaben): Visualizes plaque burden
Florbetapir F-18 (Amyvid): FDA-approved for clinical use
Amyloid load correlates poorly with cognition: Supports oligomer hypothesis

See also: [Amyloid-Beta 42/40 Ratio](/biomarkers/amyloid-beta-42-40-ratio), [Amyloid PET Imaging](/amyloid-pet-imaging), [p-tau217](/biomarkers/p-tau-217).

References

[Unknown, Hardy & Selkoe, The amyloid hypothesis of Alzheimer's disease (2002) (2002)](https://doi.org/10.1126/science.1072994)

[Unknown, O'Brien & Wong, Amyloid precursor protein processing and Alzheimer's disease (2011) (2011)](https://doi.org/10.1146/annurev-neuro-030514-124328)

[Lacor et al., Soluble oligomers of the amyloid beta-protein impair synaptic plasticity (2008) (2008)](https://doi.org/10.1093/brain/awn130)

[van Dyck et al., Lecanemab in Early Alzheimer's Disease (2023) (2023)](https://doi.org/10.1056/NEJMoa2212948)

[Unknown, Selkoe & Hardy, The amyloid hypothesis of Alzheimer's disease at 25 years (2016) (2016)](https://doi.org/10.1002/emmm.201210113)

[Unknown, Haass & Selkoe, Soluble protein oligomers in neurodegeneration (2007) (2007)](https://doi.org/10.1038/nrm2272)

[Bates et al., Aggregation of cytotoxic proteins in neurodegeneration (2019) (2019)](https://doi.org/10.1038/s41583-019-0158-9)

[Sanchez et al., Cryo-EM structures of Aβ42 fibrils from Alzheimer's disease brain (2021) (2021)](https://doi.org/10.1038/s41586-021-03796-4)

[Colvin et al., Correlative cryo-EM and NMR reveals Aβ42 polymorphism (2020) (2020)](https://doi.org/10.1016/j.neuron.2020.08.012)

[Shankar et al., Amyloid-beta protein dimers impair memory (2008) (2008)](https://doi.org/10.1073/pnas.0804173105)

[Wagner et al., Anle138b blocks Aβ oligomer formation (2019) (2019)](https://doi.org/10.1093/brain/awz085)

[Patterson et al., Lecanemab clearance and efficacy (2023) (2023)](https://doi.org/10.1038/s41591-023-02318-1)

[Simmons et al., Pyroglutamate-modified Aβ in AD (2020) (2020)](https://doi.org/10.1186/s40478-020-00947-0)

[Baker-Nigh et al., Neuronal Aβ42 accumulation in human brain (2015) (2015)](https://doi.org/10.1093/brain/awv331)

[Cline et al., Synaptic activity regulates Aβ production (2018) (2018)](https://doi.org/10.1016/j.neuron.2018.05.047)

[Palmqvist et al., Comparison of CSF and plasma Aβ42/40 ratio (2021) (2021)](https://doi.org/10.1001/jamaneurol.2021.3230)

[Jansen et al., Amyloid biomarkers in preclinical AD (2022) (2022)](https://doi.org/10.1038/s41591-022-01822-4)

[Scheltens et al., Alzheimer's disease (2021) (2021)](https://doi.org/10.1016/S0140-6736(20)

[Masters et al., Alzheimer's disease: global perspective (2019) (2019)](https://doi.org/10.1016/S0140-6736(19)

[Bateman et al., Clinical and biomarker changes (2019) (2019)](https://doi.org/10.1038/s41586-019-1665-6)

[Villemagne et al., Amyloid PET imaging in AD (2021) (2021)](https://doi.org/10.1016/j.jalz.2020.12.015)

[Unknown, Blennow & Zetterberg, Biomarkers for Alzheimer's disease (2023) (2023)](https://doi.org/10.1016/j.jalz.2023.01.003)

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Related Entities

AMYLOIDBETA

▸Metadataorigin_type: v1_polymorphic_backfill

slug	proteins-amyloid-beta
kg_node_id	AMYLOIDBETA
entity_type	protein
origin_type	v1_polymorphic_backfill
source_table	wiki_pages
wiki_page_id	wp-5a346016d4e7
__merged_from	{'merged_at': '2026-05-13', 'unprefixed_id': 'proteins-amyloid-beta'}
_schema_version	1

📊 Evidence Profile Foundational

Evidence Balance

+0%

Certainty

100%

Debates

0

Incoming

259

Outgoing

249

0 supporting 0 contradicting 0 neutral

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📗 Cite This Artifact

Amyloid-Beta (Aβ)

Amyloid-Beta (Aβ)

Amyloid-Beta (Aβ)

Amyloid-beta (Aβ)

Overview

Amyloidogenic Processing

APP Processing Pathway

Molecular Structure

Primary Sequence and Domains

Secondary and Tertiary Structure

Post-Translational Modifications

Phosphorylation

Truncation

Isomerization

Oxidation

Glycation

Aggregation and Toxicity

Nucleation-Dependent Polymerization

Aggregation Prone Regions

Soluble Oligomers: The Toxic Species

Membrane-Mediated Effects

Mechanisms of Neurotoxicity

APP Processing and Genetic Risk

Non-Amyloidogenic Pathway (Protective)

Amyloidogenic Pathway (Pathogenic)

Genetic Risk Factors

APP Mutations (Autosomal Dominant)

Protective APP Variants

APP copy number variants:

Genetic Risk Modifiers

Aβ Clearance Mechanisms

Proteolytic Degradation

Endogenous Aβ-degrading enzymes:

Microglial Clearance

Peripheral Clearance

Sleep and Glymphatic Clearance

Cellular and Animal Models

In Vitro Models

In Vivo Models

Transgenic Mouse Models

Key Findings from Models

Non-Murine Models

Clinical Trials and Therapeutic Challenges

Role in Disease

Amyloid Cascade Hypothesis

Aβ in Down Syndrome (Trisomy 21)

Therapeutic Targeting

1. Reduce Production

BACE1 Inhibitors

γ-Secretase Modulators (GSMs)

2. Enhance Clearance

Passive Immunization

Active Immunization

3. Inhibit Aggregation

Small Molecule Inhibitors

Metal Chelators

4. Target Downstream Effects

5. Emerging Approaches

Anti-Aβ Oligomer Antibodies

Aβ Degradation Enhancers

Peripheral Sink Strategies

Key Publications

External Links

Brain Atlas Resources

See Also

Aβ Peptide Variants

Major Species

Aβ42/Aβ40 Ratio

truncAβ Species

Aβ Biomarkers

Cerebrospinal Fluid (CSF) Biomarkers

Blood-Based Biomarkers

Imaging Biomarkers

References

💬 Discussion