The Apolipoprotein E Content of HDL in Cerebrospinal Fluid Is Higher in Children than in Adults

The blood-brain barrier keeps the protein concentrations in cerebrospinal fluid (CSF) much lower than in serum (1)(2)(3)(4). However, the CSF apolipoprotein E (apoE) concentration is approximately one-tenth to one-twentieth of the serum apoE concentration (5)(6)(7)(8)(9)(10)(11)(12)(13). Mainly glia cells secrete apoE in the central nervous system (14)(15)(16). CSF apoE is carried exclusively on HDL, which is the major lipoprotein in the CSF (17)(18). The CSF apoE concentration varies in neurological disorders such as central nervous system inflammatory diseases (5)(19) and Alzheimer disease (7)(8)(9)(10)(11)(12)(13). However, the clinical significance of the CSF apoE concentration is still unclear. Recent studies have suggested that the apoE content of CSF HDL is more important than the CSF apoE concentration (20). HDL enriched with apoE promotes nerve growth factor-induced neurite outgrowth (20). Because the number of synapses increases markedly in childhood (21), the apoE content of CSF HDL might be higher in children than in adults. To address this question, we measured the apoE and phospholipid (PL) concentrations in CSF simultaneously. Samples were obtained from 59 neurologically normal subjects (42 males and 17 females, ages 2–86 years). Of the 59 subjects, 30 were patients with acute leukemia in complete remission, the others were patients who underwent surgery …