Biomarkers for Alzheimer's disease to differentiate normal, SCD, and MCI subjects and their correlation with cognitive function.

INTRODUCTION: We assessed plasma biomarkers for the diagnosis of early Alzheimer's disease (AD). METHODS: Subjects were divided into three groups: cognitively unimpaired (CU) (without subjective cognitive decline [SCD]) (n = 113), CU with SCD (n = 152), and mild cognitive impairment (MCI, n = 45). Plasma assays for amyloid beta (Aβ) 40, Aβ42, neurofilament light chain protein, glial fibrillary acidic protein, and phosphorylated tau181 levels were measured using single molecule array (Simoa) technology. Neuroinflammation and blood-brain barrier (BBB) biomarkers were measured using the Corplex cytokine 10-Plex kit and the angiogenesis 6-Plex kit, respectively. RESULTS: Biomarker levels were regressed by cognitive group, age, sex, race, and apolipoprotein E apoE ε4 status, yielded significant positive associations between age and numerous AD, neuroinflammation, cytokine, and BBB plasma markers. DISCUSSION: Linear regression analysis, adjusted for age, sex, race, and ApoE status, revealed significant differences between cognitive groups in levels of several plasma biomarkers and associations with age and sex. Neuroinflammation and BBB dysfunction showed significant positive associations with age across different stages of AD.