Plasma Concentrations of Amyloid-β Peptides, BACE-1, and Tau Proteins in Alzheimer's Disease

The aim of this study was to compare, using ELISA, plasma levels of amyloid beta (Aβ)40, Aβ42, beta-site amyloid precursor protein cleaving enzyme 1 (BACE-1), total tau (t-tau), and phosphorylated tau (p-tau), as well as the Aβ42/Aβ40 ratio, between patients with Alzheimer's disease (AD) and healthy controls, and to evaluate their diagnostic performance in relation to demographic and lifestyle factors.

This study is a single-center, cross-sectional, case-control study. Twenty-four individuals diagnosed with AD and 37 healthy volunteers included in the study. Alongside the analysis of plasma samples obtained from the participants, demographic data were analyzed to assess the potential influence of lifestyle and environmental factors on disease development.

Analysis of the case data showed that increasing age was a risk factor for AD, higher education level was associated with an increased risk of AD, and tea consumption was inversely associated with AD. While age is a well-known risk factor, both the increased risk of AD associated with higher education and the relatively protective effect of tea consumption against AD are supported by the literature. Evaluation of the levels of Aβ40, Aβ42, BACE-1, t-tau, and p-tau and of the Aβ42/Aβ40 ratio revealed no significant differences between the patient and control groups. Additionally, Aβ40, Aβ42, BACE-1 showed correlations in both the control and Alzheimer's groups, whereas t-tau did not.

None of the investigated plasma biomarkers (Aβ40, Aβ42, BACE-1, t-tau, p-tau, and the Aβ42/Aβ40 ratio) discriminated Alzheimer's patients from healthy controls, with all receiver operating characteristic area under the curve values below 0.62. These findings indicate that in this cohort, plasma levels of these individual markers did not provide diagnostic value; larger longitudinal studies including cerebrospinal fluid comparisons and multi-marker panels are needed.