Blood‐based SNAP‐25 and VAMP‐2 in Alzheimer’s disease; relation to cognition, atrophy and synaptic density.

Abstract Background A hallmark of neurodegenerative disorders is synaptic dysfunction and degeneration. This makes the presynaptic protein synaptosomal‐associated protein 25 (SNAP‐25) and the Vesicle‐associated membrane protein 2 (VAMP‐2) targets of interest and importance. Previously, these proteins have only been measurable in cerebrospinal fluid (CSF) and are increased in Alzheimer’s disease (AD) patients. Considering the advancement of blood‐based detection of phosphorylated tau (p‐tau), neurofilament light (NfL) and amyloid‐β (Aβ42/40), a measure of synaptic degeneration in blood would be important for disease prognosis and clinical trial outcome. In this study, we describe results from novel single molecular arrays (Simoa) for blood SNAP‐25 and VAMP‐2. Method Prototype Simoa assays for N‐terminal SNAP‐25 and VAMP‐2 were developed as more sensitive versions of previously validated in‐house CSF assays with diluent suited for both plasma and CSF. We examined 110 participants (54 AD and 56 healthy controls) from the Swedish BioFINDER pilot study. The mean age of patients was 75.9 years (7.1 SD) and there was an even distribution of sex. We examined group differences by the Wilcoxon rank sum test and associations between these two blood biomarkers and Aβ‐PET, tau‐PET, MRI and MMSE were determined by linear regression, adjusting for age and sex. Result SNAP‐25 was significantly increased in patients with AD (mean [SD], 0.81 pg/mL [0.27]; p < 0.001) as compared to controls (0.60 pg/mL [0.22]). SNAP‐25 distinguished AD patients from controls with an area under the curve of 0.74 (95% CI = 0.65‐0.83). SNAP‐25 showed association with Aβ PET (β = 0.10, p = 0.007) but not tau PET. SNAP‐25 associated with cortical thickness (β = ‐0.05, p = 0.009) and MMSE (β = ‐6.69, p = 0.001). No significant associations were found when analysing the AD group alone. VAMP‐2 showed no significant association with any of the mentioned parameters above. Conclusion This novel ultra‐sensitive immunoassay demonstrates an increase of plasma SNAP‐25 in AD patients, and a significant relationship with cognition and cortical atrophy. Further studies will verify these changes in independent cohorts and explore the relationship between plasma SNAP‐25 and VAMP‐2 with synaptic vesicle glycoprotein 2A (SV2A) PET in a broad range of neurodegenerative disorders.