Characterization of four lipoprotein classes in human cerebrospinal fluid

Lipoprotein metabolism in brain has not yet been fully elucidated, although there are a few reports concerning lipids in the brain and lipoproteins an d apolipoproteins in the cerebrospinal fluid (CSF), To establish normal lev els of lipoproteins in human CSF, total cholesterol, phospholipids, and fat ty acids as well as apolipoprotein E (apoE) and apoA-I levels were determin ed in CSF samples from 216 individuals. For particle characterization, lipo proteins from human CSF were isolated by affinity chromatography and analyz ed for size, lipid and apolipoprotein composition. Two consecutive immunoaf finity columns with antibodies, first against apoE and subsequently against apoA-I, were used to define four distinct lipoprotein classes. The major l ipoprotein fraction consisted of particles of 13-20 nn containing apoE and apoA-I as well as apoA-IV, apoD, apoH, and apoJ. In the second particle cla ss (13-18 mn) mainly apoA-I and apoA-II but no apoE was detected. Third, th ere was a small number of large particles (18-22 mn) containing no apoA-I b ut apoE associated with apoA-IV, apoD, and apoJ, In the unbound fraction we detected small particles (10-12 nm) with low lipid content containing apoA -IV, apoD, apoH, and apoJ.jlr In summary, we established lipid and apolipop rotein levels in CSF in a large group of individuals and described four dis tinct lipoprotein classes in human CSF, differing in their apolipoprotein p attern, lipid composition, and size. On the basis of our own data and previ ous findings from other groups, we propose a classification of CSF lipoprot eins.