Apolipoprotein ε genotype modifies the association between blood‐brain barrier permeability and both grey and white matter integrity in older adults

Abstract

Background Blood‐brain barrier (BBB) permeability has been implicated in Alzheimer’s disease and is associated with decreased cerebral blood flow and cognitive impairment. However, associations between BBB permeability and structural brain changes remain unknown. This study relates the cerebrospinal fluid (CSF)/plasma albumin ratio, a proxy measure for BBB permeability, to grey matter volumes and white matter integrity Method Vanderbilt Memory and Aging Project participants free of clinical dementia or stroke (n=148, 72±6 years, 41% female, 32% apolipoprotein E (APOE) ε4 positive) underwent fasting lumbar puncture for CSF sampling and blood draw for plasma sampling. Participants underwent 3T T1‐weighted imaging to quantify grey matter volumes and diffusion tensor imaging (DTI) to quantify white matter integrity. Voxel‐wise analyses using non‐parametric permutations cross‐sectionally related the CSF/plasma albumin ratio to DTI metrics, adjusting for demographic and health variables, diagnosis, and APOE‐ε4 status. Linear regressions related the CSF/plasma albumin ratio to grey matter volumes, adjusting for identical covariates plus intracranial volume. Follow‐up models tested interactions with APOE‐ε4 status. Result In the entire sample, the CSF/plasma albumin ratio was unrelated to grey matter volumes and white matter integrity (p‐values>0.28) but interacted with APOE‐ε4 status on total grey matter (p‐value=0.02), frontal lobe (p‐value=0.01), and occipital lobe volumes (p‐value=0.04). Stratification suggested a higher CSF/plasma albumin ratio, indicating impaired BBB function, related to smaller grey matter volumes among APOE‐ε4 carriers. The CSF/plasma albumin ratio also interacted with APOE‐ε4 status on white matter integrity in the temporal and frontal lobes (p‐values<0.05), with associations present in APOE‐ε4 non‐carriers. Conclusion Increased BBB permeability is associated with decreased grey matter volume in APOE‐ε4 carriers, specifically in the frontal and occipital lobes. APOE‐ε4 may act as a vascular modifier in these regions, such that increased BBB permeability exacerbates underlying neurotoxicity and neurodegeneration. In contrast, the association between increased BBB permeability and compromised white matter integrity is driven by APOE‐ε4 non‐carriers. Taken together, these results suggest that BBB permeability may be an etiology of neurodegeneration in APOE‐ε4 carriers and highlight the importance of APOE‐ε4 status when studying BBB effects on brain health.