CHARACTERIZATION OF HUMAN PLASMA APOLIPOPROTEIN E-CONTAINING LIPOPROTEINS IN THE HIGH-DENSITY-LIPOPROTEIN SIZE RANGE - FOCUS ON PRE-BETA(1)-LPE, PRE-BETA(2)-LPE, AND ALPHA-LPE

The have used two-dimensional gel electrophoresis to separate and char acterize human plasma apolipoprotein (ape) E-containing lipoproteins i n the high density lipoprotein (HDL) size range. Lipoproteins were sep arated from whole plasma by electrophoresis (according to charge) in a 0.75% agarose gel, and then in the second dimension (according to siz e) in a 2-15% non-denaturing polyacrylamide gradient gel. ApoE-contain ing lipoproteins were detected by radiography after electrotransfer of lipoproteins to nitrocellulose membranes and incubation with I-125-la beled affinity-purified polyclonal apoE antibody. ApoE-containing lipo proteins in the HDL size range had a particle size ranging from 9 to 1 8.5 nm in diameter and could be characterized as having either gamma, pre-beta(1)-, pre-beta(2)- or alpha-electrophoretic mobility (designat ed gamma-LpE, pre-beta(1)-LpE, pre-beta(2)LpE, and alpha-LpE respectiv ely). gamma-LpE and a substantial proportion of pre-beta(1)- and pre-b eta(2)-LpE did not co-migrate with apoA-I, apoA-II, apoC-III, or apoB- 100. Subsequent experiments focused on the pre-beta(1)-LpE, pre-beta(2 )LpE, and alpha-LpE subfractions, which represented >95% of apoE in HD L-sized lipoproteins. Storage of plasma at 4 degrees C or in vitro inc ubation of plasma at 37 degrees C caused a relative decrease in pre-be ta(1)-LpE and increase in alpha-LpE. Normolipidemic patients with an a poE 2/2 phenotype tended to have increased levels of alpha-LpE, wherea s apoE 4/4 subjects tended to have a greater proportion of HDL-apoE as pre-beta(1)-LpE. Decrease in plasma HDL apoE concentration after an o ral fat load was associated with a reduction in the plasma concentrati on of all HDL-apoE subfractions. These results demonstrate that: 1) ap oE-containing HDL are heterogeneous in size and charge; 2) pre-beta(1) -LpE is a relatively labile HDL subfraction; 3) HDL-apoE subfraction d istribution is dependent on apoE phenotype; and 4) all apoE-containing HDL subfractions participate in the plasma transfer of apoE during th e postprandial period.