Alzheimer's Blood Test Detects Toxic Amyloid Possibly Years Before Symptoms Develop

University of Washington (UW) researchers have developed a laboratory test, known as SOBA (soluble oligomer binding assay), that can measure levels of amyloid beta (Aβ) peptide oligomers in blood and detect Alzheimer’s disease at all stages, including in presymptomatic cases. Results from the team’s human study indicated that the test can also differentiate Alzheimer’s from other amyloid diseases, including Parkinson’s.

“What clinicians and researchers have wanted is a reliable diagnostic test for Alzheimer’s disease—and not just an assay that confirms a diagnosis of Alzheimer’s, but one that can also detect signs of the disease before cognitive impairment happens,” said Valerie Daggett, PhD, a UW professor of bioengineering and faculty member in the UW Molecular Engineering & Sciences Institute. “That’s important for individuals’ health and for all the research into how toxic oligomers of amyloid beta go on and cause the damage that they do. What we show here is that SOBA may be the basis of such a test … “We believe that SOBA could aid in identifying individuals at risk or incubating the disease, as well as serve as a readout of therapeutic efficacy to aid in development of early treatments for Alzheimer’s disease.”

Daggett is senior author of the team’s published paper in PNAS, titled “SOBA: Development and testing of a soluble oligomer binding assay for detection of amyloidogenic toxic oligomers.” Daggett is also founder and CEO of spinout company AltPep, which is developing the technology into diagnostic and therapeutic platforms.

Amyloid diseases are associated with protein misfolding and aggregation of different toxic soluble oligomer proteins. For Alzheimer’s disease, the formation of toxic amyloid beta-peptide oligomers is an early molecular trigger before other downstream events, such as plaque deposition and abnormal tau phosphorylation, take place. “These oligomers lead to a variety of downstream effects, including impaired neuronal signaling, neuroinflammation, tau phosphorylation, and neurodegeneration, and it is estimated that these events begin 10 to 20 years before the presentation of symptoms,” the authors wrote.

The aim is to intervene early in the disease pathway, before the occurrence of irreparable damage, which may start potentially decades before clinically evident disease. However, patients today will likely receive a diagnosis of Alzheimer’s only after they exhibit well-known signs of the disease, such as memory loss. By that point, the best treatment options simply slow further progression of symptoms. “Early diagnostics and disease-modifying therapeutics for Alzheimer’s disease (AD) remain elusive,” the scientists continued.

SOBA exploits a unique property of the toxic oligomers. When misfolded amyloid beta proteins begin to clump into oligomers, they form a structure known as an alpha sheet (α–sheet). Alpha sheets are not ordinarily found in nature, and past research by the Daggett team showed that alpha sheets tend to bind to other alpha sheets. SOBA uses a synthetic α–sheet designed by the team that can bind to these α–sheet oligomers in samples of either cerebrospinal fluid or blood. The test then uses standard methods to confirm that the oligomers attached to the test surface are made up of amyloid beta proteins. “α–sheet is a nonstandard protein structure discovered in molecular dynamics (MD) simulations of a variety of amyloid-disease-associated proteins,” the scientists explained. “We reasoned that this structure may represent a unique target for early detection, and we designed stable, soluble, nontoxic α–sheet peptides to complement the α–sheet structure in the toxic species.”

The team evaluated their Alzheimer’s disease SOBA test (SOBA-AD) on 379 blood samples from 310 individuals who had previously made their blood samples and some of their medical records available for Alzheimer’s research. At the time the blood samples had been taken, the participants were recorded as having either no signs of cognitive impairment, mild cognitive impairment (MCI), Alzheimer’s disease, or another form of dementia.

The results confirmed that the SOBA assay detected Aβ toxic oligomers in patients on the Alzheimer’s disease continuum and discriminated from other forms of dementia with 99% sensitivity and 99% specificity. Interestingly, the assay identified 13 samples from the cognitively normal controls that exhibited high toxic oligomer levels. In subsequent years, the individuals for 12 of these 13 samples were confirmed to progress to mild cognitive impairment or brain pathology consistent with Alzheimer’s disease. (Follow-up was not available for one individual.) Essentially, for these 10 individuals, SOBA had detected the toxic oligomers before symptoms emerged. These results suggest that the SOBA assay can detect early Alzheimer’s disease molecular pathology prior to the development of clinical symptoms, the scientists maintain. “SOBA-AD detected the oligomers in non-cognitively impaired controls years before converting to MCI, suggesting that it may provide standalone, preclinical detection of AD,” the authors noted.

To demonstrate the broader applications of the SOBA technology, CSF samples from patients with Parkinson’s disease and Lewy body dementia were evaluated using the SOBA assay adapted for detection of Parkinson’s disease-associated toxic oligomers. The results confirmed that these tests generated strong signals and good discrimination between Parkinson’s and Alzheimer’s disease patients, confirming proof of concept of the platform’s modular and broad approach. “SOBA discriminated AD from other forms of dementia, yielding sensitivity and specificity of 99% relative to clinical and neuropathological diagnoses,” the team stated. “To explore the broader potential of SOBA, we adapted the assay for a-synuclein oligomers and confirmed their presence in CSF from patients with Parkinson’s disease and Lewy body dementia.”

Daggett’s team is working with AltPep to develop the SOBA technology into simple SOBA™ diagnostic blood tests, and into disease-modifying SOBIN™ therapeutics for amyloid diseases, which target the toxic soluble oligomers. The customized, synthetic peptides are designed to bind selectively to toxic oligomers in order to detect and neutralize them throughout disease progression. AltPep’s emphasis is on early, presymptomatic detection and treatment. Lead programs focus on Alzheimer’s and Parkinson’s diseases, with other amyloid diseases on the horizon.

“We are finding that many human diseases are associated with the accumulation of toxic oligomers that form these alpha sheet structures,” said Daggett. “Not just Alzheimer’s, but also Parkinson’s, type 2 diabetes, and more. SOBA is picking up that unique alpha sheet structure, so we hope that this method can help in diagnosing and studying many other ‘protein misfolding’ diseases.”

AltPep has received Breakthrough Designation from the FDA for its SOBA-AD diagnostic for Alzheimer’s disease. Inclusion in the FDA Breakthrough Devices Program means that AltPep can expect prioritized review of the submission of the diagnostic test.