Phospholipid transfer protein mediated conversion of high density lipoproteins generates pre β1-HDL

Abstract

High density lipoproteins (HDL) subclasses can be differentiated by two-dimensional non-denaturing polyacrylamide gradient gel electrophoresis (2D-PAGGE) and subsequent immunoblotting. The quantitatively minor HDL-subclasses pre β 1-LpA-I and γ-LpE are initial acceptors of cell-derived cholesterol into the plasma compartment. In this study we analysed the effect of phospholipid transfer protein (PLTP) on the electrophoretic distribution of HDL-subclasses in plasma as well as the ability of plasma, pre β 1-LpA-I, and γ-LpE to take up [ 3H]cholesterol from labeled fibroblasts. Pre β 1-LpA-I but not γ-LpE disappeared during a 16 hours incubation in the absence of PLTP. During a one minute incubation pre β 1-LpA-I of pre-incubated plasma released 75% less [ 3H]cholesterol from radiolabeled fibroblasts than pre β 1-LpA-I of control plasma. Pre-incubation of plasma reduced the uptake of [ 3H]cholesterol by γ-LpE by 40%. Totally, the cholesterol efflux capacity of plasma decreased by 10% compared to the original sample. The amount of immunodetectable pre β 1-LpA-I increased when plasma was incubated in the presence of PLTP while the amount of immunodetectable γ-LpE did not change. After one minute incubation of PLTP-conditioned plasma with [ 3H]cholesterol-labeled fibroblasts, the amount of radioactive cholesterol taken up by pre β 1-LpA-I was twice as high as in control plasma whereas the amount of [ 3H]cholesterol taken up by γ-LpE remained unchanged. As a net result, treatment with PLTP increased the cholesterol efflux into total plasma by 40%. Together with results of previous studies our data suggest that the conversion of α-LpA-I 3 into α-LpA-I 2 by PLTP generates pre β 1-LpA-I but not γ-LpE. PLTP helps to enhance the uptake of cell-derived cholesterol by pre β 1-LpA-1 and, thereby, the cholesterol efflux capacity of normal plasma.