Effects of diet and type IIa hyperlipoproteinemia upon structure of triacylglycerols and phosphatidyl cholines from human plasma lipoproteins.

Four normal and two individuals with Type IIa hyperlipoproteinemia were placed on the National Heart and Lung Institute Type IIa diet (low cholesterol, smaller than 300 mg/day, high polyunsaturated, low saturated fat diet) for 1 week and on a normal diet the following week. Plasma samples were obtained and the triacylglycerols, phospholipids, and cholesterol contents of plasma and of very low density lipoproteins, low density lipoproteins, and high density lipoproteins determined. Triacyglycerol fatty acid composition was determined and stereospecific analyses of triacglycerols and phosphatidyl cholines performed. Structural determinations were limited to one normal and one Type IIa individual. In normal and Type IIa individuals, chylomicrons contained twice the amount of 18:0 as did the very low density lipoproteins, low density lipoproteins, or high density lipoproteins. The structure of the triacyglycerols from the very low density lipoproteins and low density lipoproteins was asymmetric with at least 50M% 16:0 in the sn-1 position and mostly 18:1 in positions sn-2 and 3. There was a marked difference in the distribution of 18:2 in low density lipoproteins of the normal and Type IIa individuals. The control contained equal amounts of 18:2 in the sn-1 and sn-3 positions, whereas IIa low density lipoprotein was asymmetric with 26% of the 18:2 in position sn-1 and 3% in the sn-3 position. Very low density lipoprotein was asymmetric with regard to 18:2 in control and IIa samples with an average of 5% of the 18:2 in position sn-1 and 40% in position sn-3. The phosphatidyl cholines contained predominantly 16:0 and 18:0 in position sn-1, whereas the acids in position sn-2 were unsaturated with very little difference between lipoprotein classes. Neither the short dietary periods nor source of plasma affected the structure of the phosphatidyl cholines.