Lipid class and molecular species interrelationships among plasma lipoproteins of type III and type IV hyperlipemic subjects

As a further appraisal of lipoprotein interconversion and equilibration of lipid components a detailed examination was made of the chemical class and molecular species interrelationships among the major fasting plasma lipoprotein fractions within each of six male Type III and Type IV hyperlipemic subjects subsisting on free choice diets. The lipoprotein fractions were prepared by conventional ultracentrifugation and the lipid class and molecular species composition of the corresponding lipoprotein fractions were determined by gas chromatography of the intact glycerol esters and ceramides. In general, each lipoprotein fraction possessed a well defined lipid class composition, which was characterized by a dramatically decreasing triacylglycerol and increasing phospholipid and cholesteryl ester content, when progressing from the very low (VLDL) to the low (LDL) and high (HDL) density lipoproteins, as already established for normolipemic subjects. Likewise, the LDL, and LDL2 of the hyperlipemic subjects contained about two times higher proportion of total phospholipid as sphingomyelin than VLDL and HDL. Furthermore, the sphingomyelins of the HDL fraction contained about 30% more of the higher and 30% less of the lower molecular weight species than the sphingomyelins of the VLDL. Smaller differences were seen in the molecular species composition of the phosphatidylcholines, cholesteryl esters and triacylglycerols among the corresponding lipoproteins. In comparison to normolipemic subjects analyzed previously, the hyperlipemic subjects showed greater individual variability. Despite this variability the lipid class and molecular species composition in the hyperlipemic subjects was again incompatible with the hypothesis which postulates direct VLDL conversion into LDL and HDL under the influence of lipoprotein lipase and lecithin: cholesterol acyltransferase. The main differences between normolipemic and hyperlipemic plasma were found to reside in the number of the VLDL and LDL, lipoprotein particles and not in their chemical composition or physical structure, or in the apparent mechanism of their metabolic interconversion.