Interaction of very-low-density, intermediate-density, and low-density lipoproteins with human arterial wall proteoglycans

The specific interaction of lipoproteins with arterial wall constituents, particularly proteoglycans (APG), is believed to play an important role in the development of atherosclerosis. The objective of this study was to examine the interaction of apolipoprotein B (apoB) containing lipoprotein subfractions (VLDL1, S-f 60 to 400; VLDL2, S-f 20 to 60; IDL1, S-f 16 to 20; IDL2, S-f 12 to 16; LDLA, S-f 8 to 12; and LDLB, S-f 0 to 8) prepared by cumulative density gradient centrifugation with chondroitin sulfate-rich APG. Eighteen subjects were studied, and a similar pattern of interaction between the lipoprotein species and APG was found in all. The order of reactivity (as measured by increased turbidity due to insoluble complex formation) was IDL S-f 12 to 16 greater than or equal to LDL S-f 8 to 12 > LDL S-f 0 to 8 > IDL S-f 16 to 20 much greater than VLDL S-f 20 to 60 > VLDL S-f 60 to 400. When the subjects were divided on the basis of their LDL subfraction profile, the extent of insoluble complex formation was highest in the group in which small, dense LDLIII was predominant; intermediate in the group whose LDL was mainly LDLII; and lowest in the group with a high proportion of LDLI (the mean reactivity, AU at 600 nm, of APG with IDL S-f 12 to 16 and LDL S-f 8 to 12 was 0.66; 0.62 and 0.46, 0.43 and 0.20, and 0.21 for the three groups, respectively). Fibrate lipid-lowering treatment decreased the percentage of LDLIII and increased the percentage of LDLI within total LDL and reduced the reactivity of all apoB-containing lipoprotein fractions toward APG. Sialic acid content varied in different lipoprotein subfractions, being the highest in VLDL and lowest in LDL. However, across lipoprotein species, it did not significantly correlate with APG-binding reactivity, suggesting that other factors are important in determining the interaction of lipoproteins with APG. Modification of LDL arginine and lysine residues abolished the ability of the lipoprotein to interact with APG, a finding that supports the hypothesis that the interaction is dependent on key positively charged amino acids on apoB. These findings demonstrate that (1) the overall reactivity of apoB-containing lipoproteins is greatest in individuals with small, dense LDL and (2) within an individual, IDL of S-f 12 to 16 is the most reactive species, and this may in part explain the positive correlation between IDL and risk of coronary heart disease.