Plasma SNAP‐25 as a potential Alzheimer’s disease biomarker

Abstract

AbstractBackgroundSynaptic degeneration and dysfunction are hallmarks of several neurodegenerative diseases, including Alzheimer’s disease (AD). Several studies have shown that the presynaptic protein, synaptosomal‐associated‐protein‐25 (SNAP‐25), is increased in the cerebrospinal fluid (CSF) of AD patients. In the era of ultra‐sensitive immunoassays, the quantification of SNAP‐25 concentration in blood could provide an easily accessible measure of synaptic integrity in AD.MethodIn this pilot study, we investigated 42 participants (n = 23 cognitively unimpaired [CU]; n = 19 MCI or AD dementia patients [CI]) from Geneva University Hospital. A total of 27 participants underwent amyloid positron emission tomography (PET) scans and 14 underwent tau PET scans within 1 year. Global cognition was assessed with Mini Mental State Examination (MMSE). Mann‐Whitney tests were used to assess differences in plasma SNAP25 levels between diagnostic, amyloid (A+/‐) and tau (T+/‐) classification. Furthermore, we used Pearson correlations to assess the association between SNAP25, amyloid centiloid, Tau SUVr and MMSE.ResultThe mean age was 66.9 years +/‐ 7.6 years and 57% were female. SNAP‐25 was significantly increased in CI patients (0.87 pg/mL ±/‐ 0.19) compared to CU participants (0.59 pg/mL ±/‐ 0.11; p>0.001). SNAP‐25 levels were also significantly increased in A+ (0.89 pg/mL ±/‐ 0.18) and T+ (0.92 pg/mL ±/‐ 0.19) individuals compared to A‐ (0.65 pg/mL ±/‐ 0.09; p<0.001) and T‐ (0.717 pg/mL ±/‐ 0.07; p = 0.041). Moreover, we observed a significant correlation between the SNAP‐25 levels and amyloid centiloid (p = 0.016, rho = 0.48), while the correlation was not significant between SNAP‐25 and tau SUVr (p = 0.146, rho = 0.41). Finally, we observed a significant correlation between SNAP‐25 levels and MMSE score (p = 0.033, rho = ‐0.35).ConclusionThe novel plasma single molecular array (Simoa) can accurately quantify SNAP‐25 in blood plasma. In a pilot study, we observed significantly elevated plasma SNAP‐25 levels in cognitively impaired individuals and amyloid and tau positive individuals. Our findings suggest that SNAP‐25 is a potential biomarker indexing synaptic loss in AD. Further results will extend to a memory clinic cohort of >350 participants to assess its diagnostic and prognostic power and relationship to amyloid, tau, MRI and CSF biomarkers.