Higher activity of peripheral blood angiotensin-converting enzyme is associated with later-onset of Alzheimer's disease.

According to the amyloid theory, the balance between amyloid-β (Aβ) production and degradation is key to the development of Alzheimer's disease (AD). Several enzymes including angiotensin-converting enzyme (ACE) have been reported as candidate enzymes involved in Aβ degradation. We previously identified the relationship between ACE activity and AD. We present a comparison between AD and non-AD patients in the inpatient care unit of a geriatric hospital and have included the onset age and age at sampling in the comparison. We performed a colorimetric assay to determine ACE activity and a sandwich enzyme-linked immunosorbent assay (ELISA) to quantify blood plasma Aβ 1-40 and 1-42 levels. Our 676 subjects, none of whom had received ACE inhibitor medication, included 147 AD patients. Clinical diagnoses were carried out to separate subjects into the AD and non-AD groups on the basis of the criteria of the International Classification of Diseases (ICD-10) and the Consortium to Establish a Registry for AD (CERAD). We found that the later the onset of AD, the higher the ACE activity, but there was no correlation between ACE activity and the Aβ level in peripheral blood. In this report, we suggest that peripheral ACE activity may affect the age at AD onset.