Browsing by Author "Iglesias, Ángel"

Cholesteryl ester transfer protein (CETP) activity was measured in a d > 1.21 kg/L plasma fraction collected from healthy women at different times during gestation, postpartum, and in control women. CETP activity was highest in the second trimester of gestation, declined at the third trimester, and was lowest at postpartum. Only the value at the second trimester was significantly different from that of control women. This trend differed from that of circulating lipoproteins: very low-density lipoprotein (VLDL)-lipids, including triglycerides and cholesterol, increased progressively from the first to the third trimester, and then declined at postpartum. Low-density lipoprotein (LDL)cholesterol levels, like VLDL levels, rose during gestation but then remained elevated at postpartum. High-density lipoprotein (HDL)-cholesterol as well as HDL-phospholipids and apolipoprotein A-1, peaked in the second trimester, remaining elevated in the third trimester and then fell at postpartum. Finally, HDL-triglyceride increased markedly from the first to the second trimester, rose somewhat higher during the third trimester, and declined at postpartum. When all the samples from pregnant women were considered together, CETP activity correlated significantly with HDL-triglyceride levels and the changes in CETP activity during gestation and postpartum paralleled those of the HDL-triglyceride/VLDL-triglyceride ratio. These results suggest that CETP contributes to the exaggerated accumulation of triglycerides in HDL that begins in the second trimester of human gestation.

Cholesteryl ester transfer protein (CETP) activity was measured ind > 1.21 g/ml plasma from hypertriglyceridemic patients and compared with normolipidemic subjects. The assay consisted in measuring the specific transfer of [ 3 H]cholesteryl oleate from a prelabelled, apo E-poor HDL fraction to VLDL after incubation at 37°C in the presence of the d > 1.21 g/ml plasma sample: the lipoproteins were then separated by precipitation with dextran sulfate/Mg2+ solution. Increasing the volume of d > 1.21 g/ml plasma or purified human CETP in the assay produced linear responses in measured activity, whereas, either during incubation at 4°C or in the presence of rat plasma instead of human plasma, the transfer of [ 3 H]cholesteryl oleate to VLDL was not stimulated. Thus, the assay reflects changes in CETP in the sample and appears to be suitable for measuring CETP activity in d > 1.21 g/ml plasma. CETP activity was very similar in the two groups of normolipidemic subjects considered: adolescents (203 ± 11 nmol esterified cholesterol transferred per 8 h/ml plasma) and adults (215 ± 5). Patients were grouped into lipoprotein-lipase (LPL)-deficient and non-LPLdeficient according to their enzyme activity in postheparin plasma. CETP activity was highly increased in LPL-deficient, severe hyperchylomicronemic patients (430 ± 42) and was directly correlated with VLDL levels in the non-LPL-deficient individuals. Marked differences were observed in the lipid composition of HDL and apolipoprotein A-I levels among patients and controls. In the control group, CETP activity was correlated only with HDL-triglyceride and HDL-triglyceride/apo A-I mass ratio, which is compatible with the physiological role of CETP in transferring triglyceride to HDL from other lipoprotein particles. When all hypertriglyceridemic patients wen: considered together, CETP activity was inversely correlated with apo A-I and HDL-cholesterol, whereas it was directly correlated with HDL-triglyceride/HDLcholesterol and HDL-triglyceride/apo A-I mass ratios. The results indicate that the enhanced CETP activity associated with hypertriglyceridemia contributes to the compositional change of HDL, which in turn may be responsible for the reduction of HDL levels in this condition.

Liver disease is accompanied by major qualitative and quantitative disturbances in plasma lipoprotein metabolism, the extent and intensity of which depend on the degree of parenchymal damage, cholestasis, or both. The main objective of this study was to determine the cholesteryl ester transfer CETP activity and its association with the lipoprotein neutral lipid composition in patients with either liver cirrhosis or cholestasis, as compared to normal controls. Lipoproteins were isolated by ultracentrifugation, lipids and apolipoproteins were measured by conventional methods, and the fatty acid composition was established by gas chromotography; CETP activity in lipoprotein-deficient plasma was measured by determining the transfer of [3H]cholesteryl esters from HDL to VLDL. Lipoprotein lipase and hepatic lipase activities were measured in post-heparin plasma by radiochemical methods. In patients with liver cirrhosis, low levels of VLDL, HDL, apo B, and Lp(a) were observed, as well as a change in the composition of HDL particles, with increases in the relative proportion of triglyceride and free cholesterol. Respectively, the last two changes could be attributed in part to the low hepatic lipase activity observed in this study, and to the low lecithin:cholesterol acyltransferase activity previously observed by others. In patients with cholestasis, a moderate hyperlipidemia due to the elevation of LDL was found. In contrast, HDL and apo A-I levels were very low reflecting a low number of HDL particles, which also had altered compositions with increases in the triglyceride and free cholesterol contents relative to apo A-I and esterified cholesterol, respectively. As regards the fatty acid composition of lipoprotein lipids, the two groups of patients showed, in general, a lower proportion of linoleic acid and a compensating higher proportion of oleic acid as compared to the controls, changes that were observed in both cholesteryl esters and triglycerides. In contrast, the proportions of oleic and palmitoleic acids in phospholipids were increased, whereas that of stearic acid was decreased in patients as compared to controls. In patients with liver cirrhosis, as well as in controls, no changes were observed in the fatty acid compositions of cholesteryl ester, triglycerides, or phospholipids among the different lipoproteins, which probably reflects the equilibration reached by the action of CETP. In patients with cholestasis, no differences were observed in fatty acid composition among the lipoprotein phospholipids but, interestingly, cholesteryl esters from VLDL had a significantly lower linoleic acid content than those from HDL, whereas triglycerides from VLDL had significantly higher oleic acid and lower linoleic acid contents than those from HDL. This distinct fatty acid composition of the neutral lipids between lipoproteins was associated with a significant decrease (25%) in the cholesteryl ester transfer activity in patients with cholestasis. We suggest that fat malabsorption due to the biliary defect may induce a decrease in cholesteryl ester transfer protein synthesis or secretion, which in turn would slow the equilibration of the neutral lipids among plasma lipoproteins.

Human total HDL (high-density lipoprotein), HDL2 and HDL3 were labelled in vitro by incubation with lipoproteindeficient serum (LPDS) which contained either [3H)cholesteryl oleate or [14C]cholesterol under different conditions. The lipoproteins were then subfractionated by heparin-Sepharose column chromatography, and three subfractions (A, Band C) were successively eluted from each preparation of HDL, HDL2 and HDL3• When the labelling was done at 37 °C for 17 h, the subfractions were homogeneously labelled with [3H]cholesteryl oleate. However, when it was performed for only 30 min at 4 °C, the subfractions showed marked differences in the 3H specific radioactivity, which was much higher in the C fractions than in the others. 2. 3H-labelled HDL2 and HDL3 subfractions behaved differently under the precipitant action of heparin-Mn2+; fraction C (the richest in apolipoprotein E) produced the largest amount of radioactive and chemical precipitate. More 3H radioactivity, but not the cholesterol, was precipitated from HDL2 or HDL3 by the reagent, demonstrating that 3H-labelled HDL2 and HDL3 behave like their fraction C, which becomes labelled to the highest specific radioactivity despite having the smallest mass. 3. The incubation of 3H-labelled HDL subfractions with human LPDS and very-low-density lipoprotein (VLDL) at 37 °C increased the quantity of 3H radioactivity that was precipitated, in proportion to the amount of VLDL present in the media. These changes were attributable to the action of cholesterol ester transfer protein, since they did not occur at 4 °C or when human LPDS was replaced with rat LPDS. 4. Kinetics of the transfer of HDL [3H]cholesteryl oleate to VLDL showed a greater apparent V for fractions A than for fractions B from either HDL2 or HDL3, whereas the apparent Km values were very similar, whi~h suggest that this transfer process is influenced by the apoprotein composition of the donor lipoprotein.