Correlates and Predictors of Cerebrospinal Fluid Cholesterol Efflux Capacity from Neural Cells, a Family of Biomarkers for Cholesterol Epidemiology in Alzheimer's Disease

Background: Basic research has implicated intracellular cholesterol in neurons, microglia, and astrocytes in the pathogenesis of Alzheimer's disease (AD), but there is presently no assay to access intracellular cholesterol in neural cells in living people in the context of AD. Objective: To devise and characterize an assay that can access intracellular cholesterol and cholesterol efflux in neural cells in living subjects. Methods: We modified the protocol for high-density lipoprotein cholesterol efflux capacity (CEC) from macrophages, a biomarker that accesses cholesterol in macrophages in atherosclerosis. To measure cerebrospinal fluid (CSF) CECs from neurons, microglia, and astrocytes, CSF was exposed to, correspondingly, neuronal, microglial, and astrocytic cholesterol source cells. Human neuroblastoma SH-SY5Y, mouse microglial N9, and human astroglial A172 cells were used as the cholesterol source cells. CSF samples were screened for contamination with blood. CSF CECs were measured in a small cohort of 22 individuals. Results: CSF CECs from neurons, microglia, and astrocytes were moderately to moderately strongly correlated with CSF concentrations of cholesterol, apolipoprotein A-I, apolipoprotein E, and clusterin (Pearson's r = 0.53-0.86), were in poor agreement with one another regarding CEC of the CSF samples (Lin's concordance coefficient r(c) = 0.71-0.76), and were best predicted by models consisting of, correspondingly, CSF phospholipid (R-2 = 0.87, p < 0.0001), CSF apolipoprotein A-I and clusterin (R-2 = 0.90, p < 0.0001), and CSF clusterin (R-2 = 0.62, p = 0.0005). Conclusion: Characteristics of the CSF CEC metrics suggest a potential for independent association with AD and provision of fresh insight into the role of cholesterol in AD pathogenesis.