Background: Alzheimer's disease (AD) and cerebrovascular disease (CVD) including chronic small vessel disease of the brain (SVD) are the most frequent causes of dementia. AD is associated with metabolism of amyloid precursor protein (APP) and low levels of amyloid-beta peptide (Abeta) X-42 in the cerebrospinal fluid (CSF). CVD and SVD are established risk factors for AD, brain white matter lesions (WML) are established surrogate markers for SVD and are also associated with reduced CSF AbetaX-42.A cohort survey was performed to examine whether SVD or acute CVD affects APP metabolism and to explore a potential association between WML and APP metabolism in two groups; cognitively impaired patients, subjective and mild (SCI and MCI) and stroke patients. Through measurements of CSF APP metabolite levels in patients with a wide range of WML volumes, this study aimed to determine how SVD influences APP metabolism.
Methods: Sixty-three patients were included: 37 with subjective cognitive impairment (SCI) or mild cognitive impairment (MCI) without stroke, and 26 after acute stroke. Chronic and acute WML volume and infarct volume were determined by magnetic resonance imaging (MRI) post-scan processing, and CSF levels of alpha- and beta-cleaved soluble APP (sAPP-alpha and sAPP-beta, AbetaX-38, AbetaX-40 and AbetaX-42) were determined. The Mann-Whitney test was used to compare the patient groups. Chronic and acute WML volumes, infarct volume, age, and sex were used as predictors for CSF biomarker levels in linear regression analysis.
Results: CSF levels of sAPP-alpha and sAPP-beta were strongly correlated (r = 0.95, p < 0.001) and lower levels of these biomarkers were found in the stroke group than in the SCI/MCI group; median sAPP-alpha 499.5 vs. 698.0 ng/mL (p < 0.001), sAPP-beta 258.0 vs. 329.0 ng/mL (p < 0.005). CSF levels of sAPP-alpha, sAPP-beta, AbetaX-38, AbetaX-40 and AbetaX-42 were inversely correlated with chronic WML volume (p </= 0.005; p </= 0.01; p </= 0.01; p </= 0.05; p </= 0.05 respectively), but not with acute WML or infarct volumes.
Conclusions: Lower CSF levels of sAPP-alpha and sAPP-beta in the stroke group than in the SCI/MCI group and an inverse correlation with chronic WML indicate that ischemia lowers the levels of CSF sAPP metabolites and suggests that APP axonal transport or metabolism may be affected in SVD of the brain.