Influence of fat ingestion on lecithin:cholesterol acyl transfer rate in plasma of normal persons

Cholesteryl ester flux from HDL to VLDL-1 is preferentially enhanced in type IIB hyperlipidemia in the postprandial state

Postprandial triglyceride-rich lipoproteins (TRL) exert proatherogenic effects at the arterial wall, including lipid deposition. Following consumption of a mixed meal (1200 kcal), plasma-mediated cellular free cholesterol (FC) efflux, lecithin:cholesterol acyltransferase (LCAT), and cholesteryl ester transfer protein (CETP) activities were determined in subjects (n = 12) displaying type IIB hyperlipidemia and compared with those in a normolipidemic control group (n = 14). The relative capacity of plasma to induce FC efflux from Fu5AH cells via the SR-BI receptor was significantly increased 4 h postprandially (+23%; P < 0.005) in the type IIB group, whereas it remained unchanged for postprandial plasma from normolipidemic subjects. LCAT activity was significantly elevated 2 h postprandially in both the IIB and control groups, (+46% and +36%, respectively; P < 0.005 vs. respective baseline value). In type IIB subjects, total cholesteryl ester (CE) mass transfer from HDL to total TRL [chylomicrons (CMs) + VLDL-1 + VLDL-2 + IDL] increased progressively from 15 +/- 2 micro g CE/h/ml at baseline to 28 +/- 2 micro g CE transferred/h/ml (+87%; P = 0.0004) at 4 h postprandially. CE transfer to CMs and VLDL-1 was preferentially stimulated (2.6-fold and 2.3-fold respectively) at 4 h in IIB subjects and occurred concomitantly with elevation in mass and particle number of both CMs (2.3-fold) and VLDL-1 (1.3-fold). Furthermore, in type IIB subjects, CETP-mediated total CE flux over the 8 h postprandial period from HDL to potentially atherogenic TRL was significantly enhanced, and notably to VLDL-1 (32-fold elevation; P < 0.005), relative to control subjects. Such CE transfer flux was reflected in a significant postprandial increase in CE-TG ratio in both CMs and VLDL-1 in type IIB plasmas. In conclusion, HDL-CE is preferentially targeted to VLDL-1 via the action of CETP during alimentary lipemia, thereby favoring formation and accumulation of atherogenic CE-rich remnant particles.

Postprandial lipoprotein metabolism and atherosclerosis

Postprandial lipids and lipoproteins have been associated with the presence of cardiovascular disease in a large number of case-control studies. Because the metabolic perturbations around the postprandial situation is a key driving force for cholesterol flux between lipoproteins and tissues, together with the augmented generation of potentially atherogenic cholesterol-rich remnant lipoproteins, several hypotheses have been formulated to link excessive lipoproteinaemic response to fat intake with cardiovascular disease. Recent information on the regulation of lipoprotein remnant formation and its relation to atherosclerosis will enable us to test a pertinent clinical question: is there a direct relationship between repeated elevations of postprandial lipoproteins and development of atherosclerosis?

Fatty acids modulate lecithin:cholesterol acyltransferase secretion independently of effects on triglyceride secretion in primary rat hepatocytes

The regulation of plasma lecithin:cholesterol acyltransferase (LCAT) expression is not well understood. Although oleic acid increases both the secretion of triglycerides and LCAT by primary rat hepatocytes, the effect of other fatty acids (FA) on LCAT secretion is not known. This study was designed to examine the effect of FA on the hepatic secretion of LCAT, triglyceride and apolipoprotein A-1 (apoA-1). Primary rat hepatocytes were incubated with serum-free medium, supplemented with individual FA (0-1 mmol/L) for 22-24 h. Preliminary studies indicated a linear secretion of LCAT up to 24 h in both control and FA-treated cells. When hepatocytes were incubated with 1 mmol/L FA, the LCAT secretion increased 50-100% (P < 0.01) in the presence of the 18-carbon FA (stearic, oleic, elaidic and linoleic acids), whereas the presence of butyric, lauric and palmitic acids had no significant effect. LCAT secretion decreased (P < 0.01) in the presence of docosahexaenoic acid (DHA). All FA (except DHA) significantly enhanced triglyceride secretion; however, only the 18 carbon FA significantly stimulated the synthesis and secretion of apoA-1 and secretion of LCAT. The secretion of LCAT correlated with apoA-1 secretion (r = 0.88, P = 0.004) but not with triglyceride secretion (r = 0.55, P = 0.12). Treatment with oleic acid resulted in a 1.5-fold increase in hepatocyte LCAT mRNA accumulation, whereas butyrate and palmitate had no effect. These data indicate that FA that promote the apparent synthesis and secretion of apoA-1 also stimulate the secretion of LCAT in vitro, suggesting a coordinate regulatory mechanism for apoA-1 and LCAT expression.

Phospholipid-rich particles in commercial parenteral fat emulsions. An overview

In parenteral nutrition, the infusion of a fat EMU supplies both concentrated energy and covers the essential fatty acid requirements, the basic objective being to mimic as well as possible the input of chylomicrons into the blood. This objective is well met by the TAGRP of the EMU, which behave as true chylomicrons. However, commercial EMU also contain an excess of emulsifier in the form of PLRP. The number of these PLRP depends directly on the PL/TAG ratio of the EMU. They differ from the TAGRP by their composition (PL vs TAG and PL), their structure (PL in bilayer versus monolayer), and their granulometry (mean diameter 70-100 nm for PL vs 200-500 nm). The metabolic fate of the PLRP is similar in several ways to that of the TAGRP: exchanges of PL with the PL of the different cellular membranes and of the lipoproteins; captation of free CH from these same structures; and enrichment in apolipoproteins. However, because the TAGRP are the preferred substrates of the lipolytic enzymes, their clearance is much more rapid (half-life < 1 h) than that of the PLRP. As the infusion is continued, the PLRP end up accumulating and being transformed into LP-X (free CH/PL = 1; half-life of several days). As soon as the EMU is infused, the PLRP enter into competition with the TAGRP, in the lipolysis process as well as for sites of binding and for catabolism. The sites for catabolism of the two types of PAR are not the same: adipose tissues and muscles utilize the fatty acids and monoacylglycerols released by the lipolysis of the TAGRP; hepatocytes take up their remnants; the RES and the hepatocytes participate in the catabolism of the PLRP and the LP-X. Thus, prolonged infusion of EMU rich in PLRP leads to a hypercholesterolemia, or at least a dyslipoproteinemia, due to elevated LP-X, associated with a depletion of cells in CH, stimulating thus tissue cholesterogenesis. However, parenteral nutrition has evolved towards the utilization of EMU with a low PL/TAG ratio (availability of 30% formula) and less rapid delivery. For these reasons, the hypercholesterolemias that used to be observed with the 10% EMU have become much less spectacular or have even disappeared. It is interesting to note that patients on prolonged TPN, in particular those with a short small intestine, have weak cholesterolemia, reflecting a lowering of HDL and LDL not masked by elevated LP-X. At present, it seems difficult to produce sufficiently stable parenteral EMU devoid of PLRP. Notwithstanding, all the observations made since the introduction of the EMU in TPN are in favour of the use of PLRP-poor EMU. It is clear that the 10% formulas, and generally those with a PL/TAG ratio of 12/100, are ill-advised, especially in patients with a retarded clearance of circulating lipids.

The influence of cholesteryl ester content on hepatocyte triolein emulsion uptake

When triolein emulsions are enriched with cholesteryl oleate they are more readily removed by primary rat hepatocytes and HepG2 cells via an apolipoprotein E-responsive pathway. The increment in the cholesteryl ester does not appreciably change the size of the emulsion or its affinity for the apo E protein. The cholesteryl ester enriched-emulsion demonstrates increased apo E-mediated HepG2-binding as well as endocytosis. The higher the content of cholesteryl ester of the particle, the greater was both the binding and the endocytosis. The increased endocytosis was associated with increased degradation of the apo E. Cholesteryl linoleate and palmitate produced the same effects as the oleate. Lecithin-cholesterol acyltransferase additions were also able to increase the HepG2 uptake of the emulsion. The data indicates that the increment in cholesterol ester occurring during maturation of plasma triacyglycerol-rich particles facilitates hepatic remnant assimilation by an apo E-dependent pathway.

Studies on the lecithin: cholesterol acyltransferase substrate properties of HDL as determined by its subclass distribution analysed by gradient gel electrophoresis

In order to study the impact of high-density lipoproteins (HDL) subclasses on the ability of HDL to act as substrate for lecithin: cholesterol acyltransferase (LCAT), we isolated HDL from nine normolipidemic male subjects. The HDL particle size distribution was analysed by gradient gel electrophoresis and the esterification rate of the isolated homologous HDL was compared with a pool of HDL where all the nine subjects took part. It was found that the strongest determinant for HDL cholesterol esterification rate was the inhibitory action of HDL subclass 2B.

Effect of dietary carbohydrate type on lipoprotein lipase, hepatic lipase, and lecithin:cholesterol acyltransferase activities in cynomolgus monkeys

The effects of dietary sucrose and starch with and without exogenous cholesterol on postheparin plasma lipoprotein lipase (PHLA) and hepatic lipase (HLA) were studied in cynomolgus monkeys. Serum triglyceride levels were higher in sucrose-fed animals than starch and exogenous cholesterol lowered serum triglyceride levels when added to sucrose diet but not starch diets. Sucrose markedly increased insulin levels, more so than starch; however, dietary cholesterol lowered insulin levels in sucrose diet but increased the levels in starch diet. PHLA activity was increased two- to threefold greater in sucrose than in starch diets. Exogenous cholesterol lowered PHLA activity in sucrose diet but increased PHLA activity in starch diet. HLA activity was increased with sucrose more than starch. Lecithin:cholesterol acyltransferase (LCAT) activity was significantly higher in sucrose diets than in the starch diet. Addition of cholesterol to either of these diets lowered the LCAT activity. These results indicate that PHLA, HLA, and LCAT activities not only are affected by the nature of carbohydrates, but also are related to triglyceride metabolism. The interaction of carbohydrates and cholesterol in the diet by influencing these selected enzymes plays an integrated role in lipoprotein particle interconversion processes.

The effects of oral soybean phospholipid on serum total cholesterol, plasma triglyceride, and serum high-density lipoprotein cholesterol concentrations in hyperlipidemia

In a randomized, double-blind, cross-over trial soybean phospholipid and placebo, 18 g daily for 6 wk, were given orally to 20 patients on long-term treatment with standard lipid lowering diets. The effect of this treatment on serum total cholesterol and high-density lipoprotein cholesterol and plasma triglyceride was studied. After 6 wk mean (+/- SE) cholesterol concentration was decreased by 0.54 (+/- 0.19) mmol/liter in phospholipid-treated as compared to placebo-treated patients (p less than 0.02). The decrease in serum cholesterol was significant (p less than 0.02) only in patients assigned to receive phospholipid before placebo. A highly significant increase (p less than 0.001) followed the withdrawal of phospholipid. No effect on triglyceride and high-density lipoprotein cholesterol concentrations was demonstrated.

Lipid and blood pressure-lowering effect of mackerel diet in man

Fifteen healthy volunteers were put on a mackerel and herring diet, consisting of a prescribed daily isocaloric regimen in a cross-over design, for 2 weeks. Eicosapentaenoic acid (EPA - C20:5, n-3) was predominantly incorporated into cholesterol esters, whereas docosahexaenoic acid (C22:6, n-3) appeared more in serum triglycerides, indicating that the function of the latter may be different from that of EPA. After mackerel ingestion, serum triglycerides, total cholesterol and lecithin cholesterol acyl transferase (LCAT) activity were significantly decreased, returning to basal levels 3 months later. Low density lipoprotein (LDL) cholesterol, high density lipoprotein (HDL) cholesterol and postheparin lipolytic activity (PHLA) remained unchanged at the end of the mackerel diet. Generally, after the herring diet the differences were minor, only LCAT activity being significantly decreased. A markedly lower systolic and diastolic blood pressure at the end of the mackerel period could be observed. After herring diet a slight diminution of blood pressure was not significant. Accordingly, plasma noradrenaline was only significantly decreased at the end of the mackerel period. Dopamine-beta-hydroxylase (DBH) activity in serum had no differences before, during and after the study. From the data presented it can be said that a mackerel diet exerts a beneficial influence on cardiovascular risk.

Plasma lipid and lipoprotein response to fat feeding in alcoholic liver disease

Serum lipids and lipoproteins were analyzed after an overnight fast, and following a fatty meal in 10 patients with cirrhosis, 5 with fatty liver, and 5 normal subjects. Cirrhotic patients were divided into two groups of five on the basis of serum lecithin-cholesterol acyltransferase activity. Fasting triglyceride levels were similar in all four groups. In all but cirrhotic patients with low lecithin-cholesterol acyltransferase activity, most fasting triglyceride was found in very low density lipoproteins; in the latter group, most of it was found in low density lipoproteins. We confirmed that patients with fatty liver have a higher serum triglyceride response to fat feeding than normal subjects, but we did not find higher levels in cirrhotic patients. Cirrhotic patients with "normal" lecithin-cholesterol acyltransferase activity had a normal triglyceride response to dietary fat. In patients with cirrhosis and low lecithin-cholesterol acyltransferase activity, the increase in triglyceride was less than in normal subjects. In this group, most of the extra triglyceride was carried in low density lipoprotein, and not in chylomicrons and very low density lipoprotein, as in the other groups.

Effects of fasting on plasma lipids and cholesterol esterification in plasma, liver and intestinal mucosa in the char (Salmo alpinus L.)

1. CoA-dependent cholesterol esterification, measured as esterification of 3H-cholesterol, was demonstrated in homogenates of liver and intestinal mucosa of the char (Salmo alpinus L.). 2. Plasma concentration of triacylglycerols, unesterified and total cholesterol were significantly reduced to 43, 58 and 72% of the control values, respectively, after 6 weeks fasting. 3. The rate of cholesterol esterification in plasma and liver homogenate was significantly lower in the fasted fish compared to the controls, but the esterification activity in the homogenate of intestinal mucosa increased twofold in the fish fasted for 6 weeks.

Cholesterol esterification and lipids in blood plasma of the char (Salmo alpinus L.) during sexual maturation

1. The initial rate of cholesterol esterification and the concentration of triacylglycerols in plasma were generally lower in prespawning than in immature chars. No typical pattern of variation of plasma cholesterol could be observed. 2. The observed variations in plasma cholesterol esterification and lipids may be caused by reduced feeding in the prespawning period. 3. The initial rate of cholesterol esterification in plasma was positively correlated with the concentrations of triacylglycerols and unesterified cholesterol in plasma, respectively.

Lipoproteins and cholesterol esterification rate in men and women with hypercholesterolaemia of type IIa

The purpose of this study was to investigate sexual differences regarding lipoprotein concentrations and compositions, and the cholesterol esterification rate in subjects with type IIa hypercholesterolaemia. Twenty men and 33 women with type IIa hyperlipoproteinaemia, asymptomatic as regards ischaemic heart disease were investigated. Total cholesterol (TC), triglycerides (TG) and phospholipids (PL) were measured in plasma and in the very-low-density (VLDL), low-density (LDL) and high-density lipoprotein (HDL) fractions. The cholesterol esterification rate was determined in plasma in vitro. In comparison with the male group the females had higher concentrations of TC and PL in the HDL, leading to higher ratios of HDL-TC/LDL-TC and HDL-PL/LDL-Pl in the females group. The cholesterol esterification rates were equal in the sexes. However, relations between the cholesterol esterification rates and lipoprotein concentrations and between cholesterol esterification rates and overweight were not equal in the sexes. The higher HDL-TC concentration and HDL-TC/DL-TC ratio in women than in men with type IIa might partly explain the lower female morbidity in cardiovascular disease.

Lipoproteins and plasma cholesterol esterification in normal and diabetic subjects

Serum lipoproteins, separated by preparative ultracentrifugation and the activity of the plasma enzyme lecithin: cholesterol acyltransferase (LCAT) have been measured in insulin-dependent diabetics, non-insulin-dependent diabetics and in age-matched non-diabetic controls. In the insulin-dependent diabetics, mean total serum cholesterol and high density lipoprotein cholesterol (HDL-C) concentrations were significantly higher than in controls. Non-insulin-dependent diabetics had significantly raised total triglycerides and cholesterol, but HDL-C levels were essentially normal. The increased low density lipoprotein cholesterol (LDL-C) in both diabetic groups was statistically significant in men. A methodological study of HDL separation techniques was carried out to facilitate interpretation of these findings. Mean LCAT activity, by a method reflecting combined enzyme and substrate effects was significantly increased in these diabetic groups. The results confirm recent reports of a raised HDL-C in those insulin-dependent diabetics who are prone to coronary heart disease.

Acute dietary effects on plasma lipids, lipoproteins and lipolytic enzymes in healthy normal males

Diurnal plasma lipids and lipoproteins were studied in twelve healthy young males on corn oil and palm oil diets, respectively. The major triglyceridy. Lecithin-cholesterol acyl transferase, lipoprotein lipase and hepatic triglyceride lipase were also measured. diurnal changes of triglycerides and cholesterol were confined to lipoproteins of d less than 1.006 kg/l. There was a diurnal rise of lecithin-cholesterol acyl transferase activity with corn oil but not with palm oil. Fasting and postprandial postheparin lipoprotein lipase and hepatic triglyceride lipase were similar but there was a significant correlation of postprandial hepatic lipase with postprandial plasma triglycerides on palm oil. Marked diurnal changes of triglyceride fatty acids were observed not only in 'very low density lipoprotein' but also in high-density lipoprotein amounting to approximately one third of total high density lipoprotein triglyceride fatty acids.

Initial cholesterol esterification rate in hyperlipoproteinaemia: effects of triglyceride-rich lipoproteins

The initial cholesterol esterification rate (LCAT activity) was determined in ninety-four hyperlipidaemic subjects. LCAT activity was elevated in hypertriglyceridaemia, whereas patients with hypercholesterolaemia had normal activities. In hypertriglyceridaemic subjects LCAT activity correlated with the concentrations of d less than 1.006 lipoproteins, plasma triglycerides, cholesterol and cholesterol esters and phospholipid levels. Addition of d less than 1.006 lipoprotein to normal plasma resulted in a dose dependent stimulation of enzyme activity with a sigmoidal response curve. When the d less than 1.006 lipoproteins were removed from hypertriglyceridaemic plasma by ultracentrifugation, the enzyme activity in the residual d greater than 1.006 fraction dropped, but still was higher than in normal plasma and correlated with the amount of d less than 1.006 lipoproteins originally present. Thus, high LCAT activity in hypertriglyceridaemia cannot be explained solely by the presence of an increased d less than 1.006 lipoprotein concentration. An increase of enzyme concentration or changes in concentration or composition of other lipoproteins (high density lipoproteins) may contribute to the high LCAT activity in hypertriglyceridaemia.