Postprandial lipemia differentially influences high density lipoprotein subpopulations LpAI and LpAI,AII

High-fat meal effect on LDL, HDL, and VLDL particle size and number in the Genetics of Lipid-Lowering Drugs and Diet Network (GOLDN): an interventional study

Background

Postprandial lipemia (PPL) is likely a risk factor for cardiovascular disease but these changes have not been well described and characterized in a large cohort. We assessed acute changes in the size and concentration of total and subclasses of LDL, HDL, and VLDL particles in response to a high-fat meal. Participants (n = 1048) from the Genetics of Lipid-Lowering Drugs and Diet Network (GOLDN) Study who ingested a high-fat meal were included in this analysis. Lipids were measured at 0 hr (fasting), 3.5 hr, and 6 hr after a standardized fat meal. Particle size distributions were determined using nuclear magnetic resonance spectroscopy. Analyses were stratified by baseline triglycerides (normal vs. elevated) and gender. The effect of PPL on changes in lipoprotein subclasses was assessed using repeated measures ANOVA.

Results

Postprandially, LDL-C, HDL-C, VLDL-C, and triglycerides increased regardless of baseline triglyceride status, with the largest increases in VLDL-C and TG; however, those with elevated triglycerides demonstrated larger magnitude of response. Total LDL particle number decreased over the 6-hour time interval, mostly from a decrease in the number of small LDL particles. Similarly, total VLDL particle number decreased due to reductions in medium and small VLDL particles. Large VLDL particles and chylomicrons demonstrated the largest increase in concentration. HDL particles demonstrated minimal overall changes in total particle number.

Conclusions

We have characterized the changes in LDL and VLDL particle number, and their subclass patterns following a high-fat meal.

Postprandial modulation of serum paraoxonase activity and concentration in diabetic and non-diabetic subjects

OBJECTIVES

To analyse the HDL associated anti-oxidant enzyme paraoxonase-1, during postprandial hyperlipaemia.

METHODS AND RESULTS

Type 2 diabetic patients (n=72), glucose intolerant patients (n=10) and controls (n=38) consumed a high fat:high carbohydrate meal. Blood samples were collected up to 4h and analysed for lipids and paraoxonase-1. In vitro studies examined HDL function with respect to the enzyme. There were significant postprandial increases in serum triglycerides. Paraoxonase-1 activity decreased significantly throughout the postprandial phase. Concentrations of the enzyme initially decreased significantly, but returned to fasting concentrations at 4h. Specific activities were significantly lower at 4h, compared to fasting. The decrease in specific activity was linked to the dynamic phase of postprandial lipoprotein metabolism. Apo AI limited loss of paraoxonase-1. HDL isolated after being subjected to postprandial conditions in vitro had reduced capacity to associate with and stabilise PON1.

CONCLUSIONS

Postprandial hyperlipaemia was associated with changes to serum paraoxonase-1, consistent with a reduced anti-oxidant potential of HDL. No differences were observed between diabetic and non-diabetic patients, suggesting that the effect was linked to postprandial hyperlipaemia. Modifications to paraoxonase-1 could contribute to increased risk of vascular disease associated with postprandial lipaemia, particularly in diabetic patients, who are already deficient in serum paraoxonase-1.

The concept of apolipoprotein-defined lipoprotein families and its clinical significance

Classification of plasma lipoproteins on the basis of apolipoprotein (apo) composition recognizes two lipoprotein (Lp) classes, one of which is characterized by apoA-I and the other by apoB as major protein constituents. The former lipoprotein class consists of three major subclasses referred to (according to their apolipoprotein constituents) as Lp-A-I, Lp-A-I:A-II, and Lp-A-II, and the latter one of five subclasses called Lp-B, Lp-B:E, Lp-B:C, Lp-B:C:E, and Lp-A-II:B:C:D:E. As polydisperse systems of particles, the apoA-I-containing lipoproteins overlap in high-density segments and apoB- containing lipoproteins in low-density segments of the density gradient. Each subclass is characterized by a specific chemical composition and metabolic property. Normolipidemia and dyslipoproteinemias are characterized by quantitative rather than qualitative differences in the levels of apoA- and apoB-containing subclasses. Furthermore, apoA-containing subclasses seem to differ with respect to their relative antiatherogenic capacities, and apoB-containing subclasses regarding their relative atherogenic potentials. Whereas Lp-A-I may have a greater antiatherogenic capacity than other apoA-containing subclasses, the cholesterol-enriched Lp-B:C appears to be the most atherogenic subclass among apoB-containing lipoprotein families. The use of pharmacologic and/or dietary interventions to treat dyslipoproteinemias has already shown that these therapeutic modalities may affect selectively individual apolipoprotein-defined lipoproteins, and thus allow the selection of individualized treatments targeted at decreasing harmful and/or increasing beneficial lipoprotein subclasses.

Apolipoprotein A-II, HDL metabolism and atherosclerosis

Apolipoprotein (Apo) A-I and apo A-II are the major apolipoproteins of HDL. It is clearly demonstrated that there are inverse relationships between HDL-cholesterol and apo A-I plasma levels and the risk of coronary heart disease (CHD) in the general population. On the other hand, it is still not clearly demonstrated whether apo A-II plasma levels are associated with CHD risk. A recent prospective epidemiological (PRIME) study suggests that Lp A-I (HDL containing apo A-I but not apo A-II) and Lp A-I:A-II (HDL containing apo A-I and apo A-II) were both reduced in survivors of myocardial infarction, suggesting that both particles are risk markers of CHD. Apo A-II and Lp A-I:A-II plasma levels should be rather related to apo A-II production rate than to apo A-II catabolism. Mice transgenic for both human apo A-I and apo A-II are less protected against atherosclerosis development than mice transgenic for human apo A-I only, but the results of the effects of trangenesis of human apo A-II (in the absence of a co-transgenesis of human apo A-I) are controversial. It is highly suggested that HDL reduce CHD risk by promoting the transfer of peripherical free cholesterol to the liver through the so-called 'reverse cholesterol transfer'. Apo A-II modulates different steps of HDL metabolism and therefore probably alters reverse cholesterol transport. Nevertheless, some effects of apo A-II on intermediate HDL metabolism might improve reverse cholesterol transport and might reduce atherosclerosis development while some other effects might be deleterious. In different in vitro models of cell cultures, Lp A-I:A-II induce either a lower or a similar cellular cholesterol efflux (the first step of reverse cholesterol transport) than Lp A-I. Results depend on numerous factors such as cultured cell types and experimental conditions. Furthermore, the effects of apo A-II on HDL metabolism, beyond cellular cholesterol efflux, are also complex and controversial: apo A-II may inhibit lecithin-cholesterol acyltransferase (LCAT) (potential deleterious effect) and cholesteryl-ester-transfer protein (CETP) (potential beneficial effect) activities, but may increase the hepatic lipase (HL) activity (potential beneficial effect). Apo A-II may also inhibit the hepatic cholesteryl uptake from HDL (potential deleterious effect) probably through the SR-BI depending pathway. Therefore, in terms of atherogenesis, apo A-II alters the intermediate HDL metabolism in opposing ways by increasing (LCAT, SR-BI) or decreasing (HL, CETP) the atherogenicity of lipid metabolism. Effects of apo A-II on atherogenesis are controversial in humans and in transgenic animals and probably depend on the complex effects of apo A-II on these different intermediate metabolic steps which are in weak equilibrium with each other and which can be modified by both endogenous and environmental factors. It can be suggested that apo A-II is not a strong determinant of lipid metabolism, but is rather a modulator of reverse cholesterol transport.

Evidence for a cholesteryl ester donor activity of LDL particles during alimentary lipemia in normolipidemic subjects

Postprandial hypertriglyceridemia represents an independent risk factor for coronary artery disease. In the postprandial state, elevated levels of triglyceride-rich lipoproteins (TRL) are minor acceptors of HDL-cholesteryl ester (CE) transferred by CETP in normolipidemic subjects: indeed, LDL particles represent the major CE acceptors. In order to evaluate further the potential atherogenicity of lipoprotein particles characteristic of the postprandial phase in normolipidemic subjects, we determined the quantitative and qualitative features of apoB- and apoAI-containing lipoproteins over an 8-h period following consumption of a mixed meal. During postprandial lipemia, we observed a significant decrease (-12%) in plasma AI concentration (138+/-4 and 156+/-4 mg/dl, at 3 h and baseline, respectively, P<0.005). Concomitantly, a progressive increase (+13%) was detected in HDL2 concentrations (138+/-7 mg/dl at 4 h vs. 122+/-12 mg/dl at baseline, P<0.005), as well as a significant reduction (-9%) in HDL3 levels (137+/-6 mg/dl at 3 h vs. 150+/-4 mg/dl at baseline; P<0.05). Additionally, plasma LDL was reduced by 5% (247+/-12 mg/dl at 3 h vs. 260+/-15 mg/dl at baseline; P<0.05) 3 h following meal intake. Moreover, a significant reduction (-10%) occurred in the CE/TG ratio in LDL at 2 h postprandially (8+/-2 at 2 h vs. 9+/-3 at baseline; P<0.005). These changes reflected an increment (17+/-3 mg/dl at 3 h vs. 15+/-4 mg/dl at baseline; P<0.05) in LDL triglyceride concentrations. Despite the high CE acceptor capacity of LDL particles, no measurable increase in their CE content was detected during the postprandial phase. We demonstrated that CE accepted by LDL particles from HDL are secondarily transferred to chylomicrons by CETP. As chylomicrons displayed a 260-fold lower CE/TG ratio than LDL (0.03:1 and 7.8:1 in chylomicrons and LDL, respectively), CE-rich LDL may act to donate CE to chylomicrons. In conclusion, our data indicate that the presence of elevated levels of chylomicrons induces LDL to act as a secondary donor of CE during the postprandial phase.

Independent effects of Apo E phenotype and plasma triglyceride on lipoprotein particle sizes in the fasting and postprandial states

LDL particle sizes and Apo E phenotypes were determined in 212 subjects of whom 51 had angina. LDL diameter was significantly less in subjects with an epsilon2 allele (24.76+/-0.08 vs 24.94+/-0.02 nm, P=0.02), and this was evident for both E2/E3 (24.77+/-0.09 nm) and E2/E4 (24.69+/-0.08 nm) phenotypes. Although there was a negative relation between LDL diameter and plasma triglyceride, the effect of apo E2 was still evident with adjustment for triglyceride. In multiple regression analysis, the significant determinants of LDL diameter were gender (with females having larger particles than males), body mass index, and the presence (or absence) of E2. HDL particle sizes and compositions were determined on fasting samples and, additionally, 5 and 8 hours after a fat-rich meal for 48 coronary heart disease cases and 49 control subjects. Fasting HDL particle sizes were not related to the presence of E2 but were significantly smaller for subjects possessing an epsilon4 allele (8. 09+/-0.08 vs 8.39+/-0.05 nm, P=0.003) and were negatively related to plasma triglyceride. However, the effect of E4 persisted after adjustment for triglyceride. In a multiple regression analysis, the only significant determinant of fasting HDL diameter was the presence (or absence) of E4 with fasting plasma triglyceride just failing to reach significance (P=0.06). There was a postprandial increase in HDL diameter that was less marked in subjects with coronary heart disease. The postprandial increase in HDL diameter was of sufficient magnitude to result in size reclassification of HDL particles. The influence of E4 was also evident at both postprandial time points. Compositional analysis demonstrated that the increase in HDL diameters postprandially could be attributed to triglyceride enrichment, with an accompanying fall in cholesterol ester content. Phospholipid changes postprandially were biphasic with an initial fall followed by a rise in concentration. The increase in triglyceride content was significantly less in those subjects with angina despite an equivalent rise in plasma triglyceride. The present study demonstrates significant, but different, effects of variation in apo E phenotype on the particle sizes of both HDL and LDL. Such effects were still evident with adjustment for differences in plasma triglyceride and suggests that variation in apo E phenotype exerts effects on lipoprotein particle sizes by mechanisms additional to those dependent on change in plasma triglyceride.

Postprandial responses of plasma lipids and lipoproteins in subjects with apoA-I(Lys107-->0)

Subjects with apoA-I(Lys107-->0) deletion mutation have reduced levels of plasma HDL cholesterol, apoA-I, apoA-II and Lp(AI:AII). In the present study were describe the postprandial responses of apoA-I(Lys107-->0) subjects (n=6) to the ingestion of a fat rich meal compared to the responses of their unaffected family members (n=6). The postprandial plasma triglyceride responses were comparable in the two groups of subjects. Plasma postprandial HDL cholesterol levels fell in both groups; patients (0.89+/-0.05-0.76+/-0.06 mmol/l, P=0.0032) and control subjects (1.32+/-0.25-1.18+/-0.21 mmol/l; P=0.0022). HDL2 cholesterol levels tended to rise, but the changes were not significant. By contrast, in both patients and control subjects, the HDL3 cholesterol levels fell; patients (0.52+/-0.15-0.37+/-0.11 mmol/l, P=0.0068) and control subjects (0.63+/-0.10-0.49+/-0.08 mmol/l, P=0.0078), respectively. In both patients and control subjects the plasma HDL2 mass increased in response to the fat meal; patients (94.7+/-37.3-114.3+/-28.8 mg/dl, P=0.0397) and control subjects (142.1+/-32.8-168.1+/-29.8 mg/dl, P=0.0298), whereas HDL3 mass decreased; patients (162.3+/-36.8-131.4+/-28.9 mg/dl, P=0.0251) and control subjects (185.5+/-34.1-161.1+/-29.0 mg/dl, P=0.0021), respectively. In control subjects the triglyceride levels increased in both HDL2 (0.10+/-0.06-0.17+/-0.06 mmol/l; P=0.0005) and to a lesser extent in HDL3 (0.10+/-0.03-0.12+/-0.02 mmol/l, P=0.0017). In patients, triglyceride levels in both HDL subclasses remained unchanged. Changes in the concentration of Lp(AI) in HDL2 and HDL3 were comparable in the two groups of subjects. The Lp(AI:AII) concentration in HDL2 remained unchanged in the patients, but increased in control subjects (change+27%. P=0.0026). Consequently, the 20% difference at baseline in the concentration of Lp(AI:AII) in HDL2 between the patients and control subjects increased postprandially to 45% (P=0.0240). The Lp(AI:AII) concentration in HDL3 decreased in both groups, but the changes were non-significant. Our findings show that in postprandial state, no accumulation of triglycerides in HDL subclasses occurs in patients with apoA-I(Lys[107]-->0) and that these patients appear to lack the ability to respond to fat feeding by increasing the Lp(AI:AII) concentration in HDL2.

Cholesterol efflux, cholesterol esterification, and cholesteryl ester transfer by LpA-I and LpA-I/A-II in native plasma

HDLs encompass structurally heterogeneous particles that fulfill specific functions in reverse cholesterol transport. Two-dimensional nondenaturing polyacrylamide gradient gel electrophoresis (2D-PAGGE) of normal plasma and subsequent immunoblotting with anti-apolipoprotein (apo) A-I antibodies differentiates an abundant particle with electrophoretic alpha-mobility and less abundant particles with electrophoretic pre-beta-mobility (pre beta 1-LpA-I, pre beta 2-LpA-I, pre beta 3-LpA-I). Immunodetection with anti-apoA-II antibodies identifies a single particle with alpha-mobility. To differentiate alpha-migrating HDL without apo A-II (alpha-LpA-I) from those with apoA-II (alpha-LpA-I/A-II), we combined 2D-PAGGE with immunoadsorption of apoA-II. Incubation of plasma with [3H]cholesterol-labeled fibroblasts in combination with immunosubtracting 2D-PAGGE allowed us to analyze the role of alpha-LpA-I and alpha-LpA-I/A-II in the uptake and esterification of cell-derived cholesterol in native plasma. Depending on the duration of incubations with cells, alpha-LpA-I took up two to four times more [3H]cholesterol than alpha-LpA-I/A-II. Irrespective of the duration of incubation, two to three times more [3H]cholesteryl esters accumulated in alpha-LpA-I than in alpha-LpA-I/A-II. Subsequent incubations in the presence of an inhibitor of lecithin:cholesterol acyltransferase led to preferential accumulation of [3H]cholesteryl esters in alpha-LpA-I/A-II. In conclusion, our data indicate that alpha-LpA-I is more effective than alpha-LpA-I/A-II in both uptake and esterification of cell-derived cholesterol. Moreover, alpha-LpA-I/A-II appears to accumulate cholesteryl esters, at least partially, from alpha-LpA-I.