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Two electrophoretic populations of very low density lipoprotein are frequently observed in both normal and hyperlipidemic human sera. This gives the appearance of two pre-beta bands, called the "double pre-beta lipoprotein phenomenon." The slow and fast bands forming the double pre-beta lipoprotein were isolated by ultracentrifugation in the zonal rotor under rate flotation conditions. On the basis of the effluent position, the slow band showed a lower flotation coefficient than the fast one. The lipid and apoprotein composition of the two very low density lipoprotein populations isolated by zonal ultracentrifugation was in close agreement with those obtained by preparative agarose gel electrophoresis. The slow and fast pre-beta fractions had the same triglyceride fatty acid composition. Both fractions contained only higher molecular weight apo B-100, while the slow fraction was relatively enriched in apo E and apo C-lll. Since the slow pre-beta fraction showed the typical properties of the remnant particle, studying this fraction could clarify the possible relationship between remnant lipoproteins and atherogenesis. Zonal rotor ultracentrifugation may be useful to characterize remnant particles in normal and hyperlipidemic subjects. (Arteriosclerosis 4:598-603, November/December 1984) T wo separate populations of very low density lipoprotein (VLDL) that showed fast and slow prebeta mobility upon agarose gel electrophoresis were isolated by preparative agarose gel electrophoresis and characterized in our laboratory in 1977. 1The lipid and protein composition of the slow moving pre-beta component is similar to that of remnant particles because the slow moving component is poor (contains a low amount) in triglycerides and apo C and it is rich (contains a high amount) in cholesteryl esters and arginine-rich proteins.However, it should be stressed that these two VLDL particles are clearly distinguishable from the beta VLDL of dysbetalipoproteinemia (Type III) be- cause of two main characteristics: 1) the electrophoretic mobility of the VLDL particles is strictly pre-beta rather than beta, and 2) the isoelectric focusing (IEF) pattern of the apoprotein E in the VLDL particles is normal. The separation and characterization of remnant particles similar to those presented by double prebeta lipoproteinemia (DPBL), sometimes called late pre-beta lipoproteinemia, 2 is important because of the possible relationships between remnant particle accumulation and the development of atherosclerosis. Clinical studies show a very high prevalence of DPBL in uremia and hypothyroidism, conditions that are frequently associated with atherosclerotic complications.*- 5The present study was undertaken to find a faster and simpler method than the one we had previously used (preparative agarose gel electrophoresis 1 ) to isolate these two electrophoretic VLDL populations. We found that zonal rotor ultracentrifugation under flotation conditions enabled us to indirectly calculate the flotation coefficients of the two VLDL components and to mea...

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Type V hyperlipoproteinaemia is a disorder of lipid transport characterized by the accumulation in serum of chylomicrons and very low density lipoproteins. The purpose of the study was the analysis of serum lipids and lipoproteins by ultracentrifugation in nine patients with primary type V hyperlipoproteinaemia before and during dietary treatment. After 30 days of balanced isocaloric diet mean serum triglycerides fell from 25.4 +/- 15.0 (mean +/- SD) to 2.8 +/- 1.7 mmol l-1. At the same time the chylomicrons and the very low density lipoproteins of flotation rate higher than 100 disappeared from the serum while the remaining very low density lipoproteins maintained unaltered their normal protein-lipid composition. After 30 days the low density lipoproteins increased significantly in concentration (from 1.6 +/- 0.8 to 4.1 +/- 1.1 mmol l-1 cholesterol) and their percentage content of cholesterol and triglyceride was increased and reduced, respectively. The highest concentration of intermediate density lipoprotein cholesterol was observed after 15 days of treatment (1.2 +/- 0.6 mmol l-1. The abnormally low concentrations and the physicochemical properties of the high density lipoproteins remained unchanged throughout the study (from 0.6 +/- 0.2 to 0.8 +/- 0.2 mmol l-1 cholesterol concentration) and no high density lipoproteins two (HDL2) were observed at any time. The effects of this treatment were an increase in low density and marginal change in high density lipoproteins which are considered, respectively, a positive and a negative risk factor for atherosclerosis.