| Abstract: | Low-density lipoproteins (density = 1.019-1.063 g/ml) were isolated in 10 subjects with type V hyperlipoproteinemia by ultracentrifugation in a zonal rotor under rate flotation conditions. Plasma LDL concentrations in these patients were extremely reduced, as well as being heterogeneous, and two different subclasses consisting of LDL2 (density = 1.019-1.045 g/ml) and LDL3 (density = 1.045-1.063 g/ml) were observed. LDL2 and LDL3 have similar electrophoretic mobilities in beta position in agarose gel, and their diameters, calculated from gel filtration studies, were inversely proportional to their densities. LDL2 and LDL3 have a mean hydrated density of 1.034 and 1.054 g/ml, respectively. In comparison with normal LDL2, the LDL2 and LDL3 of hypertriglyceridemic subjects are particularly rich in triacylglycerols and poor in cholesteryl esters and free cholesterol, while they have an increasing amount of proteins. The protein moiety is composed almost exclusively of apolipoprotein B-100 in IDL, LDL2 and LDL3 ; in addition, IDL also contain apolipoprotein C peptides. This characterization of LDL heterogeneity in type V hyperlipoproteinemia should be considered in interpreting kinetic data in human normal and pathological lipid metabolism and in evaluating the atherogenic risk of hypertriglyceridemia. |
