Influence of an atherogenic diet on the structure of swine low density lipoproteins

Abstract

Five groups of three swine each were fed a basal diet supplemented with 15% tallow and either 0.0, 1.0, 1.5, 2.0%, or 2.5% cholesterol. The animals were studied over a period of 9 weeks to observe changes in plasma lipids and low density lipoproteins (LDL). At the end of the study period, LDL was analyzed by rate zonal ultracentrifugation, characterized chemically, and examined by differential scanning calorimetry. Within 3 weeks of initiation of the cholesterol-supplemented diets, there was an increase in the plasma levels of cholesterol and total LDL. LDL from swine fed the basal diet and the basal diet plus 1.0% cholesterol appeared in two LDL populations (LDL1 and LDL2) when analyzed by rate zonal ultracentrifugation. After diets containing 1.5, 2.0, and 2.5% dietary cholesterol, there was an increase in the mean flotation rate of total LDL which shifted to a lower density. LDL1 from the high cholesterol diets had a decreased triglyceride content when compared to those of the low cholesterol diets. When examined by differential scanning calorimetry, the LDL1 from the animals fed at least 1.5% cholesterol had phase transitions above body temperature, whereas the LDL from those fed 0 and 1.0% cholesterol had phase transitions below 37 degrees C. In contrast, the thermal behavior and fatty acid compositions of the extracted cholesteryl esters of the LDL obtained after the five different diets were not remarkably different. Since LDL triglyceride and cholesteryl esters are predicted to coexist in a common phase in the LDL core, the different thermal behavior of the LDL obtained after diets with different cholesterol contents is due to differences in triglyceride content which are a secondary effect of cholesterol-feeding. From these data we conclude that dietary cholesterol increases plasma LDL content, decreases LDL triglyceride content, and alters the particle structure. These changes in lipoprotein structure may contribute to the known development of atherosclerosis in cholesterol-fed swine.