title: Novel route for elimination of brain oxysterols across the blood-brain barrier: conversion into 7alpha-hydroxy-3-oxo-4-cholestenoic acid.
abstract: Recently, we demonstrated a net blood-to-brain passage of the oxysterol 27-hydroxycholesterol corresponding to 4-5 mg/day. As the steady-state levels of this sterol are only 1-2 mug/g brain tissue, we hypothesized that it is metabolized and subsequently eliminated from the brain. To explore this concept, we first measured the capacity of in vitro systems representing the major cell populations found in the brain to metabolize 27-hydroxycholesterol. We show here that 27-hydroxycholesterol is metabolized into the known C(27) steroidal acid 7alpha-hydroxy-3-oxo-4-cholestenoic acid by neuronal cell models only. Using an in vitro model of the blood-brain barrier, we demonstrate that 7alpha-hydroxy-3-oxo-4-cholestenoic acid is efficiently transferred across monolayers of primary brain microvascular endothelial cells. Finally, we measured the concentration of 7alpha-hydroxy-3-oxo-4-cholestenoic acid in plasma from the internal jugular vein and brachial artery of healthy volunteers. Calculation of the arteriovenous concentration difference revealed a significant in vivo flux of this steroid from the brain into the circulation in human. Together, these studies identify a novel metabolic route for the elimination of 27-hydroxylated sterols from the brain. Given the emerging connections between cholesterol and neurodegeneration, this pathway may be of importance for the development of these conditions.
authors.affiliation: Division of Clinical Chemistry, Karolinska University Hospital, Huddinge, Sweden.
authors.forename: Steve
authors.initials: S
authors.lastname: Meaney
authors.forename: Maura
authors.initials: M
authors.lastname: Heverin
authors.forename: Ute
authors.initials: U
authors.lastname: Panzenboeck
authors.forename: Lena
authors.initials: L
authors.lastname: Ekström
authors.forename: Magnus
authors.initials: M
authors.lastname: Axelsson
authors.forename: Ulla
authors.initials: U
authors.lastname: Andersson
authors.forename: Ulf
authors.initials: U
authors.lastname: Diczfalusy
authors.forename: Irina
authors.initials: I
authors.lastname: Pikuleva
authors.forename: John
authors.initials: J
authors.lastname: Wahren
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Sattler
authors.forename: Ingemar
authors.initials: I
authors.lastname: Björkhem
mesh_terms: D001692:Biological Transport; D001812:Blood-Brain Barrier / Q000378:metabolism*; D001921:Brain / Q000378:metabolism*; D001923:Brain Chemistry; D002783:Cholestenones / Q000378:metabolism; D006801:Humans; D006888:Hydroxycholesterols / Q000378:metabolism*; D008954:Models, Biological
chemical_list: D002783:Cholestenones; D006888:Hydroxycholesterols; C056891:7 alpha-hydroxy-3-oxo-4-cholestenoic acid; C076996:27-hydroxycholesterol