Biochemical characterization of pre-beta 1 high-density lipoprotein from human ovarian follicular fluid: evidence for the presence of a lipid core

Abstract

In order to isolate pre-beta 1 HDL, we have focused our interest on a particular model, namely, human preovulatory follicular fluid, which contains only HDL as a lipoprotein class as well as a high proportion of pre-beta 1 HDL relative to total HDL (1.5 times more than in homologous plasma) as evidenced by double-dimension gel electrophoresis. Apo A-I in pre-beta 1 HDL represented 17.6% of total apo A-I. Stokes' radii corresponded to 3.42 nm in follicular fluid pre-beta 1 HDL and 3.48 nm in homologous plasma counterparts. After electroelution from agarose, pre-beta 1 HDL were isolated in amounts sufficient to allow characterization by size-exclusion chromatography using HPLC. The estimated apparent molecular mass of these particles is 61.6 kDa. Lipid composition of pre-beta 1 HDL evidenced a low lipid content compared to follicular fluid HDL isolated by ultracentrifugation. Phospholipid composition showed a dramatic decrease in phosphatidylcholines (40.5% of total phospholipids), and the presence of lysophosphatidylcholines and of acidic phospholipids such as phosphatidylserine and phosphatidylinositol (13.6 and 13.7%, respectively). Furthermore, cholesteryl ester and triacylglycerol molecules were quantified by gas-liquid chromatography and represented 8-9% of the pre-beta 1 HDL total weight. Thus, a lipid core is present in pre-beta 1 HDL, which would be compatible with a spherical shape. The follicular fluid appears to be a good model to a better understanding of HDL metabolism.