Amyloid Proteins Are Regulated in a Circadian Pattern
Amyloid-beta levels in CSF increased in a linear fashion over 36 hours, but the increase was smaller among patients with Alzheimer’s disease than among controls, according to Yafei Huang, PhD, postdoctoral research scholar at Washington University in St. Louis. Amyloid-beta levels did not increase in plasma.
Circadian fluctuations of amyloid-beta levels in plasma and CSF were twice as great among younger patients than among older patients. The degree of fluctuation did not differ greatly between older patients with Alzheimer’s disease and older patients without Alzheimer’s disease, however. The researchers found no correlation between amyloid-beta levels in CSF and those in plasma.
To understand the dynamics of CSF and plasma amyloid-beta levels during the course of the day, Dr. Huang studied three groups of participants. The first group included 80 patients with amyloid deposition and an average age of 72. The second group included age-matched controls, and the third group included healthy controls with an average age of 36. The investigators collected CSF and plasma samples from the participants every hour for 36 hours and measured the amyloid-beta levels in the samples.
“There is a very poor correlation between plasma and CSF amyloid-beta levels,” said Dr. Huang. “Plasma amyloid-beta levels are not good surrogate markers for CSF amyloid-beta levels,” she added. “When we use amyloid-beta levels as biomarkers, we have to keep this in mind. Time of sampling is very important, too.”
—Erik Greb