Search

The purpose of the study was an assessment of the lipid and protein composition of very low density lipoproteins (VLDL) in hyperlipoproteinaemias type IIa, IIb, III and IV. Besides that, cholesterol was determined in low density lipoproteins (LDL) and high density lipoproteins (HDL). Fifty-seven patients with idiopathic hyperlipoproteinaemia and nineteen subjects without lipid metabolism disturbances were studied. The VLDL fraction was obtained by ultracentrifugation of the serum. The LDL and HDL fractions were separated by precipitation. A raised value of the LDL:HDL cholesterol ratio was found in hyperlipoproteinaemias type IIb, III and IV. Positive correlations between the concentrations of lipid and protein components of the VLDL fraction were found in hyperlipoproteinaemias type IIa, IIb, IV and in normolipaemia, which suggests maintained proportions between VLDL components. The high proportion of cholesterol in the VLDL fraction in relation to other components in type III hyperlipoproteinaemia indicates an abnormal composition of this fraction.

The purpose of this study was an assessment of the relative proportions of apolipoprotein C subfractions in the VLDL fraction, which could contribute to explaining the development of metabolic disturbances in hyper-pre-beta-lipoproteinaemias. The study was carried out in 21 patients with hyperlipoproteinaemia type IIa, IIb, III, IV and in 8 subjects without lipid metabolism disturbances. Apolipoproteins C were separated in disc electrophoresis on polyacrylamide gel (PAGE) with added 8-M of urea. After the electrophoresis three main subfractions were obtained and were identified according to their electrophoretic mobility as Apo CII, Apo CIII1 and Apo CIII2. The relative per cent proportions of apolipoproteins C were determined by densitometry. A correlation was found between triglyceride concentration in the VLDL fraction and the relative amounts of Apo CII and Apo CIII1. Moreover, a raised ratio of the lipoprotein lipase inhibitor (Apo CIII1) to the activator of this enzyme (Apo CII) was demonstrated in hyperlipoproteinaemias type IIb, III and IV, which may suggest decreased susceptibility of these lipoproteins to the action of lipoprotein lipase.

Twenty two patients with hyperlipoproteinaemia type IV consumed fructose in a daily dose of 80 g for 28 days. Apart from that they kept their normal diet. We observed the considerable heterogeneity of hyperlipaemic responses of patients under study after 7 days of fructose feeding. However VLDL-TG and the relative ratio apo CIII1/apo CII in VLDL increased in the whole group. The rise in serum VLDL was associated with a fall in LDL-Chol and HDL-Chol. After extention of fructose intake to 28 days a decrease of VLDL-TG with concomitant fall of the relative ratio apo CIII1/apo CII in VLDL was found. LDL-Chol increased. Our observations point to the reversibility of fructose-induced changes in the lipoprotein composition after prolongation of its intake.

Following incubation of the VLDL isolated from hypertriglyceridaemic patients with normal human postheparin plasma VLDL remnants were obtained. 125I-VLDL remnants were taken up and catabolized by mouse macrophages in vitro. This was a receptor-dependent process. Unlabelled VLDL remnants added to the incubation medium inhibited the degradation of 125I-VLDL remnants in the cells. This could not be produced by the presence of VLDL or acetyl-LDL in the medium. It shows that mouse macrophages bind VLDL remnants by means of an other receptor than that for acetyl-LDL. The cell cholesterol content increased after incubation of the cells with VLDL remnants or acetyl-LDL, but not with native VLDL or LDL.

After 30 days of clofibrate administration to 11 patients with type IV hyperlipoproteinemia, a significant fall was observed in serum triglyceride and cholesterol levels. In the VLDL fraction the concentrations of triglycerides, cholesterol and apo B were significantly decreased. The apo CII/apo CIII ratio was raised. Cholesterol concentration changes in LDL and HDL fractions were not significant.