COMPOSITIONAL DIFFERENCES OF LDL PARTICLES IN NORMAL SUBJECTS WITH LDL SUBCLASS PHENOTYPE-A AND LDL SUBCLASS PHENOTYPE-B

A predominance of small LDL particles (subclass phenotype B), as deter mined by gradient-gel electrophoresis is found among patients with myo cardial infarction. Despite physical differences in phenotype A and B particles, differences in lipid composition of particles in these phen otypes have yet to be reported in an unselected population of mates an d females. The present study used lipid/apoB ratios to analyze the amo unt of lipid per LDL particle, isolated by density-gradient ultracentr ifugation, in 70 healthy subjects. Relative to apoB, the LDL particles from phenotype B subjects were found to contain less free cholesterol (0.391+/-0.05 versus 0.465+/-0.05; mean+/-SD; P<.001), phospholipid ( 1.26+/-0.2 versus 1.43+/-0.2; P<.001), and cholesteryl ester (1.97+/-0 .1 versus 2.11+/-0.2; P<.001) than particles from phenotype A subjects . The amount of triglyceride per LDL particle did not differ between t he two phenotypes (0.410+/-0.1 versus 0.406+/-0.1; P=NS) despite highe r plasma triglyceride levels in the phenotype B subjects. LDL size and buoyancy were positively correlated with particle free cholesterol, p hospholipid, and cholesteryl ester but not with particle triglyceride. These data suggest that the physical properties of LDL from subjects with phenotype A and B reflect their lipid composition. The compositio nal differences between LDL particles of the two phenotypes may provid e new insight into the increased risk of myocardial infarction in subj ects with small, dense LDL.