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The overlooked candidate is P3, also called amyloid alpha (Aα), a peptide made when cells process amyloid precursor protein (APP) through an alternative pathway. A 2026 ChemBioChem perspective reports that P3 can form oligomers, fibrils and amyloid deposits, may be neurotoxic, and can interact with amyloid beta (Aβ). These are biochemical findings—not proof that P3 causes Alzheimer’s disease in patients.
What P3 (amyloid alpha) is
P3 is not a newly discovered pathogen, supplement or diagnostic test. It is a fragment of APP, the same parent protein that can generate Aβ. For decades, scientists generally treated P3 as a soluble, nonamyloidogenic by-product that was unlikely to harm neurons.
Jevgenij A. Raskatov of the University of California, Santa Cruz, challenges that assumption in “Amyloid Alpha: The Neglected Cousin of Amyloid Beta,” first published in ChemBioChem on February 27, 2026. The perspective argues that P3 deserves consideration in models of Alzheimer’s biology alongside Aβ.
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The difference begins with the enzyme that cuts APP first:
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- Aβ route: β-secretase cuts APP, followed by γ-secretase. This produces Aβ peptides.
- P3 route: α-secretase cuts APP first, followed by γ-secretase. This produces P3, or Aα.
P3 lacks the first 16 amino acids of Aβ. Those missing residues contain many water-solubilizing amino acids, which helped establish the expectation that P3 would remain soluble and harmless. Raskatov’s argument is that this expectation needed to be tested rather than assumed.
What the 2026 findings report
P3 forms amyloid structures
Raskatov’s perspective summarizes roughly five years of work by his group. In laboratory experiments, P3 reportedly “readily forms oligomers and fibrils.” The group also found that P3 can form deposits at least as readily as Aβ and can aggregate more rapidly under the tested conditions.
Oligomers are small assemblies of peptide molecules; fibrils are larger, thread-like assemblies that can accumulate into deposits. These structures are important because different assemblies can have different biological effects. Demonstrating that P3 aggregates in vitro does not establish that the same amount, structure or distribution occurs in a human Alzheimer’s brain.
P3 may affect neurons and Aβ
The reported experiments indicate that P3 is potentially neurotoxic, although the toxicity measured by the group was lower than Aβ’s in the comparisons described. The studies also reported physical interaction between P3 and Aβ. Their co-interaction changed how the peptides aggregated and altered toxicity in the laboratory systems.
The perspective says an independent laboratory in the United Kingdom validated and extended the findings. It does not yet establish the precise toxicity mechanism or the extent to which these reactions matter in patients. Possible mechanisms under investigation include membrane poration, production of reactive oxygen species and inflammatory responses.
“The P3 peptide is, most likely, not the innocent bystander it was commonly thought to be. There’s still more research to be done. But this could turn Alzheimer’s research on its head,” Raskatov said in a University of California, Santa Cruz, report.
How the Aβ-only and expanded models differ
| Question | Aβ-focused model | Expanded model including P3/Aα |
|---|---|---|
| Initial APP cleavage | β-secretase, then γ-secretase | α-secretase, then γ-secretase for P3; the Aβ route remains present |
| Peptide structure | Aβ products retain the N-terminal region absent from P3 | P3 lacks Aβ’s first 16 amino acids |
| Aggregation in laboratory studies | Aβ forms oligomers, fibrils and deposits | P3 also forms oligomers and fibrils; the reported group studies found faster aggregation and deposits at least as readily as Aβ |
| Relative neurotoxicity | Aβ is the established comparator in these experiments | P3 is potentially neurotoxic, with lower toxicity than Aβ in the reported group comparisons |
| Peptide interaction | Often modeled without a major P3 contribution | P3 and Aβ can physically interact and change one another’s aggregation and toxicity |
| Evidence in human Alzheimer’s tissue | Aβ is extensively studied in patient tissue | How much P3 is present in Alzheimer’s deposits, and how to distinguish it from Aβ there, remains unresolved |
David Teplow, emeritus professor of neurology at UCLA, called the reevaluation consequential for both basic science and clinical work on Alzheimer’s causes and treatments. The proposed change is an expansion of the amyloid model, not evidence that Aβ has been disproved.
Why the overlooked peptide matters
Aβ has been the principal Alzheimer’s drug target for decades. The ChemBioChem perspective cites more than 400 mostly unsuccessful Alzheimer’s clinical trials, most aimed at Aβ. It also cites an annual worldwide economic burden of more than $818 billion and approximately 35 million people living with Alzheimer’s disease globally, with the population projected to double by 2050. The University of California, Santa Cruz, account gives the rounded figure of more than $800 billion in annual cost and notes that some Aβ-directed programs produced modest benefit alongside serious adverse effects.
Those figures describe the scale of the disease and the difficulty of developing treatments; they are not measurements of P3’s effect. If P3 changes Aβ aggregation or contributes its own toxic assemblies, experiments that measure only Aβ could miss part of the biology. That possibility could help explain why a single-target strategy has not produced consistent clinical success, but it is not, by itself, an explanation for failed trials.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What has not been proved
- No evidence in these sources shows that P3 causes Alzheimer’s disease in humans.
- The amount of P3 in patient brains, its location in deposits and its relationship to disease stage are not established.
- No study cited here shows that reducing P3 improves memory, cognition or survival.
- The reported aggregation and toxicity results come primarily from biochemical and laboratory models, not a clinical treatment trial.
- P3 is not shown to be more dangerous than Aβ in patients; the reported group comparisons found lower toxicity for P3, while still identifying a potential harmful effect.
Raskatov has emphasized that the finding should be tested rather than treated as a final answer. As he put it, “P3 is a distinct aggregating peptide that is itself potentially neurotoxic and may be contributing to Alzheimer’s disease.”
Can P3 be targeted with a treatment?
There is no approved P3-targeted therapy established by these findings. Before a drug strategy could be evaluated, researchers would need reliable methods to distinguish Aα from Aβ in human brain deposits, determine whether P3 levels track with pathology, identify which assemblies are harmful and test whether changing P3 alters disease-related outcomes.
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Potential intervention concepts could include blocking P3 formation, preventing its aggregation, disrupting P3–Aβ co-assemblies or reducing downstream cellular damage. Each remains a hypothesis. A treatment that removes one peptide could also affect APP processing and other cellular functions, so safety and mechanism would have to be demonstrated experimentally.
How to read the headline
The strongest defensible interpretation is that scientists may have overlooked a biologically active APP fragment. P3/Aα can aggregate in laboratory conditions, may damage neurons, and can modify Aβ behavior. The work broadens the questions Alzheimer’s researchers should ask; it does not identify a single hidden cause, overturn the amyloid hypothesis or provide a patient-ready therapy.
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