title: Factors influencing interaction of human plasma low-density lipoproteins with discoidal complexes of apolipoprotein A-I and phosphatidylcholine.
abstract: The effect of plasma components on the particle size distribution and chemical composition of human plasma low-density lipoproteins (LDL) during interaction with discoidal complexes of human apolipoprotein A-I and phosphatidylcholine (PC) was investigated. Incubation (37 degrees C, 1 h and 6 h) of LDL with discoidal complexes in the presence of the plasma ultracentrifugal d greater than 1.20 g/ml fraction (activity of lecithin-cholesterol acyltransferase inhibited) produces an increase in LDL apparent particle diameter two-to six-fold greater than that observed in the absence of the plasma d greater than 1.20 g/ml fraction. In incubation mixtures of LDL and discoidal complexes, both in the presence and absence of the plasma d greater than 1.20 g/ml fraction, the extent of LDL apparent particle diameter increase is: (1) approximately three-fold greater at 6 h than at 1 h, and (2) markedly greater for LDL with initially small (22.4-24.0 nm) major components than for LDL with initially large (26.2-26.8 nm) major components. The facilitation factor in the plasma d greater than 1.20 g/ml fraction is not plasma phospholipid transfer protein. Purified human serum albumin produces an apparent particle diameter increase comparable to the plasma d greater than 1.20 g/ml fraction. The discoidal complex-induced increase in LDL apparent particle diameter value by albumin is associated with an increase in phospholipid uptake by LDL and a decreased loss of LDL unesterified cholesterol. In preliminary experiments, high-density lipoproteins (HDL) reverse the apparent particle diameter increase originally induced by discoidal complexes. The presence of HDL (HDL phospholipid/LDL phospholipid molar ratio of 10:1) in the incubation (6 h) mixture of LDL and discoidal complexes also attenuates LDL apparent particle diameter increase. In vivo, the plasma LDL/HDL ratio may be a controlling factor in determining the extent to which phospholipid uptake and the associated change in LDL particle size distribution occurs.
mesh_terms: D016632:Apolipoprotein A-I; D001054:Apolipoproteins A / Q000494:pharmacology*; D002352:Carrier Proteins / Q000494:pharmacology; D006801:Humans; D008075:Lipoproteins, HDL / Q000032:analysis; D008077:Lipoproteins, LDL / Q000097:blood*; D008565:Membrane Proteins; D010316:Particle Size; D010713:Phosphatidylcholines / Q000494:pharmacology*; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids / Q000032:analysis; D012709:Serum Albumin / Q000494:pharmacology
chemical_list: D016632:Apolipoprotein A-I; D001054:Apolipoproteins A; D002352:Carrier Proteins; D008075:Lipoproteins, HDL; D008077:Lipoproteins, LDL; D008565:Membrane Proteins; D010713:Phosphatidylcholines; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D012709:Serum Albumin