Stability of Plasma Amyloid-β 1–40, Amyloid-β 1–42, and Total Tau Protein over Repeated Freeze/Thaw Cycles
Huei‐Chun Liu, Ming‐Jang Chiu, Chin‐Hsien Lin, Shieh‐Yueh Yang
Abstract
<b><i>Introduction:</i></b> Blood biomarkers of Alzheimer’s disease (AD) have attracted much attention of researchers in recent years. In clinical studies, repeated freeze/thaw cycles often occur and may influence the stability of biomarkers. This study aims to investigate the stability of amyloid-β 1–40 (Aβ<sub>1–40</sub>), amyloid-β 1–42 (Aβ<sub>1–42</sub>), and total tau protein (T-tau) in plasma over freeze/thaw cycles. <b><i>Methods:</i></b> Plasma samples from healthy controls (<i>n</i> = 2), AD patients (AD, <i>n =</i>3) and Parkinson’s disease patients (PD, <i>n</i> = 3) were collected by standardized procedure and immediately frozen at –80°C. Samples underwent 5 freeze/thaw (–80°C/room temperature) cycles. The concentrations of Aβ<sub>1–40</sub>, Aβ<sub>1–42</sub>, and T-tau were monitored during the freeze/thaw tests using an immunomagnetic reduction (IMR) assay. The relative percentage of concentrations after every freeze/thaw cycle was calculated for each biomarker. <b><i>Results:</i></b> A tendency of decrease in the averaged relative percentages over samples through the freeze and thaw cycles for Aβ<sub>1–40</sub> (100 to 97.11%), Aβ<sub>1–42</sub> (100 to 94.99%), and T-tau (100 to 95.65%) was found. However, the decreases were less than 6%. For all three biomarkers, no statistical significance was found between the levels of fresh plasma and those of the plasma experiencing 5 freeze/thaw cycles (<i>p</i> &#x3e; 0.1). <b><i>Conclusions:</i></b> Plasma Aβ<sub>1–40</sub>, Aβ<sub>1–42</sub>, and T-tau are stable through 5 freeze/thaw cycles measured with IMR.