Plasma Levels of Phosphorylated Tau 181 Are Associated With Cerebral Metabolic Dysfunction in Cognitively Impaired Individuals

Background

Alzheimer’s disease (AD) biomarkers are primarily evaluated through MRI, PET, and CSF methods in order to diagnose and monitor disease. Recently, advances in the assessment of blood-based biomarkers have shown promise for simple, inexpensive, accessible, and minimally invasive tools with diagnostic and prognostic value for AD. Most recently, plasma phosphorylated tau181 (p-tau181) has shown excellent performance. The relationship between plasma p-tau181 and cerebral metabolic dysfunction assessed by [¹⁸F]FDG PET in AD is still unknown.

Methods

This study was performed on a total of 892 individuals (297 cognitively unimpaired; 595 cognitively impaired) from the ADNI cohort. Plasma p-tau181 was assessed using single molecular array (Simoa) technology and metabolic dysfunction was indexed by [¹⁸F]FDG PET. Cross-sectional associations between plasma and CSF p-tau181 and [¹⁸F]FDG were assessed using voxelwise linear regression models, with individuals stratified by diagnostic group and by Aβ status. Associations between baseline plasma p-tau181 and longitudinal rate of brain metabolic decline were also assessed in a subset (n=389) of individuals using correlations and voxelwise regression models.

Results

Plasma p-tau181 was elevated in Aβ+ and cognitively impaired individuals as well as in APOE ε4 carriers, and was significantly associated with age, worse cognitive performance, and CSF p-tau181. Cross-sectional analyses showed strong associations between plasma p-tau181 and [¹⁸F]FDG PET in Aβ+ and cognitively impaired individuals. Voxelwise longitudinal analyses showed that baseline plasma p-tau181 concentrations were significantly associated with annual rates of metabolic decline only in cognitively impaired individuals, bilaterally in the medial and lateral temporal lobes.

Conclusions

The associations between plasma p-tau181 and reduced brain metabolism, primarily in cognitively impaired and in Aβ+ individuals, supports the use of plasma p-tau181 as a simple, low-cost, minimally invasive, and accessible tool to both assess current and predict future metabolic dysfunction associated with AD, comparatively to PET, MRI, and CSF methods.