Associations between cerebrospinal fluid biomarkers and brain regions of relevance for very early Alzheimer’s disease processes

Background The relation between cerebrospinal fluid (CSF) biomarkers of Alzheimer’s disease (AD) and neurodegeneration and brain regions of relevance for very early pathological processes in AD is poorly understood. This study aims to investigate cross-sectional associations between the CSF biomarkers amyloid-β1-42 (Aβ42), total-tau (T-tau), phosphorylated-tau (P-tau), neurogranin (Ng) and neurofilament light (NfL) protein and normalized intracranial volumes of the hippocampus, amygdala, entorhinal cortex and basal forebrain observed on structural magnetic resonance imaging (MRI) in cognitively healthy 70-year olds from the general population. Method The analyses included 226 cognitively normal individuals (clinical dementia rating of zero), examined during 2014-2016 as part of the population-based Gothenburg H70 Birth Cohort Studies in Sweden. The study participants had undergone lumbar puncture examination to extract CSF samples for biomarker measurements (pg/mL), MRI scan (volumes in mm³), and apolipoprotein E (APOE) genotyping. Linear regressions, adjusted for sex, were used to examine potential associations. Result Elevated CSF T-tau, P-tau, and Ng concentrations were associated with smaller volumes of the hippocampus, amygdala, and entorhinal cortex among individuals with amyloid pathology (p = 8×10−8 – 0.04) and among APOE ε4 carriers (p = 8×10−5 – 0.04). In addition, elevated CSF T-tau, P-tau, and Ng concentrations were associated with larger basal forebrain among individuals without pathological Aβ42 (p = 0.001 – 0.01) and among APOE ε4 non-carriers (p = 0.004 – 0.02). Conclusion The results of our study suggest that among cognitively normal adults who have amyloid pathology or genetic susceptibility to AD, there are associations between axonal degeneration, tangle pathology, and synapse loss and decreased volumes of AD vulnerable brain regions. The associations between elevated CSF biomarkers and larger basal forebrain in cognitively normal individuals were unexpected, but could possibly be explained by compensatory mechanisms or an inflammatory response (generating neuronal or glial swelling) as a very early reaction to the presence of increased levels of tau and Ng. Our findings highlight the clinical pathophysiological relevance of CSF biomarkers of AD and neurodegeneration and how they relate to AD specific brain regions seen on structural MRI in 70-year-olds that may be at risk to develop dementia.