Roles of CYP27 and CYP46 in transport of cholesterol from extrahepatic organs to the liver. Cholesterol does not pass readily across the blood-brain barrier, but cholesterol produced in the brain can be oxidized by CYP46 to form the more soluble species 24S-hydroxycholesterol. Likewise, 27-hydroxycholesterol is formed in other extrahepatic cells and contributes to the net flow of circulating oxysterols from other organs to the liver (10).