Plasma apolipoproteins and lipoproteins are purified for a diverse series of studies including structural analysis, cell culture studies, and human as well as animal kinetic studies. Lipoprotein particles with defined apolipoprotein composition are isolated by affinity chromatography and Fast Protein Liquid Chromatography. Current studies are focused on the role of LpE particles in intravascular cholesterol transport and cholesterol efflux from cells. ApoE plays a central role in lipoprotein metabolism as a ligand for the LDL and LRP receptors. ApoE containing lipoprotein particles have been isolated from control subjects and patients with abetalipoproteinemia. In human plasma LpE particles are heterogeneous and include LpE, LpE:A-I, LpE:A-I:A-II. The isolated LpE particles have been used to determine the plasma kinetics of the individual LpE particles and the evaluate the efficiency of these particles to promote cholesterol efflux. Kinetic studies in control subjects established that the fractional catabolic rate of LpE>LpE:A-I>LpE:A-I:A-II. Cholesterol efflux from cholesterol loaded normal fibroblasts revealed that LpE only particles did not promote efflux while LpE:A-I and LpE:A-I:A-II particles effectively promoted efflux. LpE:A-I and LpA-I:A-II lipoprotein particles have also been isolated by FPLC from LCAT transgenic mice. Several lines of evidence have established that HDL in LCAT transgenic mice is abnormal and not effective in reverse cholesterol transport. The isolated HDL lipoprotein particles from LCAT transgenic mice have been shown in cell culture systems to effectively efflux membrane cholesterol but to have a reduced ability to initiate translocation of intracellular cholesterol.
