SOBA: Development and testing of a soluble oligomer binding assay for detection of amyloidogenic toxic oligomers

Abstract

The formation of toxic Amyloid β-peptide (Aβ) oligomers is one of the earliest events in the molecular pathology of Alzheimer’s Disease (AD). 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 y before the presentation of symptoms. Toxic Aβ oligomers contain a nonstandard protein structure, termed α-sheet, and designed α–sheet peptides target this main-chain structure in toxic oligomers independent of sequence. Here we show that a designed α–sheet peptide inhibits the deleterious effects on neuronal signaling and also serves as a capture agent in our soluble oligomer binding assay (SOBA). Pre-incubated synthetic α–sheet-containing Aβ oligomers produce strong SOBA signals, while monomeric and β-sheet protofibrillar Aβ do not. α–sheet containing oligomers were also present in cerebrospinal fluid (CSF) from an AD patient versus a noncognitively impaired control. For the detection of toxic oligomers in plasma, we developed a plate coating to increase the density of the capture peptide. The proof of concept was achieved by testing 379 banked human plasma samples. SOBA detected Aβ oligomers in patients on the AD continuum, including controls who later progressed to mild cognitive impairment. In addition, SOBA discriminated AD from other forms of dementia, yielding sensitivity and specificity of 99% relative to clinical and neuropathological diagnoses. 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.

New Pathways Identify Novel Drug Targets for the Prevention and Treatment of Alzheimer’s Disease

“…The application of a new blood test, a not complicated binding assay, has recently been published for very early detection of soluble toxic Aβ peptides (SOBA) [ 115 ]. Further studies should demonstrate the suitability of the SOBA method for identifying patients at risk of cognitive decline.…”

The role of α-sheet structure in amyloidogenesis: characterization and implications

“…Based on this discrimination between different Aβ conformers (figure 9 b,c ), we explored the detection of toxic oligomers in biological fluids, including cerebrospinal fluid (CSF) and blood. SOBA was able to distinguish between individuals with mild cognitive impairment and moderate to severe AD from non-cognitively impaired controls in both CSF and plasma [84]. The generality of the approach was tested by modifying SOBA to detect α-sheet containing α-synuclein oligomers in samples from patients with PD with excellent discrimination between control and PD cases [84].…”

“…SOBA was able to distinguish between individuals with mild cognitive impairment and moderate to severe AD from non-cognitively impaired controls in both CSF and plasma [84]. The generality of the approach was tested by modifying SOBA to detect α-sheet containing α-synuclein oligomers in samples from patients with PD with excellent discrimination between control and PD cases [84].…”

“…(b) Aβ42 spiked into PBS and evaluated by SOBA.Monomer is at beginning of aggregation reaction; toxic oligomers, incubated 24 h; and protofibrils, incubated 120 h (times correspond to (a)). (c) CD spectra for time points tested on SOBA assay[84]. Figures are taken from[9] and[84].…”

Aβ*56 is a stable oligomer that correlates with age-related memory loss in Tg2576 mice

“…Aβ*56 is but one of many variants of brain-derived Aβ oligomers. Other brain-derived, oligomeric variants include dimers and trimers 3 , prefibrillar oligomers that bind A11 antibodies 4 , amylospheroids 5 , globulomers 6 , fibrillar oligomers that bind OC antibodies 7 , protofibrillar oligomers that bind mAb158/lecanumab antibodies 8 , intraneuronal oligomers that bind NU-1 anti-ADDL antibodies 9 , annular protofibrils 10 , amyloid pores 11 , oligomers that bind crenezumab 12 , oligomers that bind aducanumab 13 , oligomers that bind ACU3B3/ACU193 anti-ADDL antibodies 14 , oligomers that bind α-sheets 15 , and oligomers that bind JD1 antibodies 16 , whose structure, spatial distribution, temporal expression, biogenesis, and effects on brain function are topics of active study with important therapeutic implications.…”