Elevation of plasma soluble amyloid precursor protein beta in Alzheimer's disease

Abstract

Introduction: Beta-amyloid is considered to be a pathophysiological marker in Alzheimer's disease (AD). Soluble amyloid precursor proteins (sAPPs)-alpha (sAPP alpha) and -beta (sAPP beta), which are the byproducts of non-amyloidogenic and amyloidogenic process of APP, respectively, have been repeatedly observed in the cerebrospinal fluids (CSF) of AD patients. The present study focused on the determination of sAPP levels in peripheral blood. Methods: The plasma protein levels of sAPP alpha and sAPP beta were measured with ELISA. Plasma from 52 AD patients, 98 amnestic mild cognitive impairment (MCI) patients, and 114 cognitively normal controls were compared. Results: The plasma level of sAPP beta was significantly increased in AD patients than in cognitively healthy controls. However, no significant change in plasma sAPP alpha was observed among the three groups. Furthermore, the plasma sAPP beta levels significantly correlated with cognitive assessment scales, such as clinical dementia rating (CDR), and mini-mental status examination (MMSE). Interestingly, sAPP alpha and sAPP beta had a positive correlation with each other in blood plasma, similar to previous studies on CSF sAPP. This correlation was stronger in the MCI and AD groups than in the cognitively healthy controls. Conclusions: These results suggest that individuals with elevated plasma sAPP beta levels are at an increased risk of AD; elevation in these levels may reflect the progression of disease.