Independent effects of Apo E phenotype and plasma triglyceride on lipoprotein particle sizes in the fasting and postprandial states.

LDL particle sizes and Apo E phenotypes were determined in 212 subjects of whom 51 had angina. LDL diameter was significantly less in subjects with an epsilon2 allele (24.76+/-0.08 vs 24.94+/-0.02 nm, P=0.02), and this was evident for both E2/E3 (24.77+/-0.09 nm) and E2/E4 (24.69+/-0.08 nm) phenotypes. Although there was a negative relation between LDL diameter and plasma triglyceride, the effect of apo E2 was still evident with adjustment for triglyceride. In multiple regression analysis, the significant determinants of LDL diameter were gender (with females having larger particles than males), body mass index, and the presence (or absence) of E2. HDL particle sizes and compositions were determined on fasting samples and, additionally, 5 and 8 hours after a fat-rich meal for 48 coronary heart disease cases and 49 control subjects. Fasting HDL particle sizes were not related to the presence of E2 but were significantly smaller for subjects possessing an epsilon4 allele (8. 09+/-0.08 vs 8.39+/-0.05 nm, P=0.003) and were negatively related to plasma triglyceride. However, the effect of E4 persisted after adjustment for triglyceride. In a multiple regression analysis, the only significant determinant of fasting HDL diameter was the presence (or absence) of E4 with fasting plasma triglyceride just failing to reach significance (P=0.06). There was a postprandial increase in HDL diameter that was less marked in subjects with coronary heart disease. The postprandial increase in HDL diameter was of sufficient magnitude to result in size reclassification of HDL particles. The influence of E4 was also evident at both postprandial time points. Compositional analysis demonstrated that the increase in HDL diameters postprandially could be attributed to triglyceride enrichment, with an accompanying fall in cholesterol ester content. Phospholipid changes postprandially were biphasic with an initial fall followed by a rise in concentration. The increase in triglyceride content was significantly less in those subjects with angina despite an equivalent rise in plasma triglyceride. The present study demonstrates significant, but different, effects of variation in apo E phenotype on the particle sizes of both HDL and LDL. Such effects were still evident with adjustment for differences in plasma triglyceride and suggests that variation in apo E phenotype exerts effects on lipoprotein particle sizes by mechanisms additional to those dependent on change in plasma triglyceride.