Composition of human low density lipoprotein: effects of postprandial triglyceride-rich lipoproteins, lipoprotein lipase, hepatic lipase and cholesteryl ester transfer protein

VIIaAT complexes, procoagulant phospholipids, and thrombin generation during postprandial lipemia

INTRODUCTION

Factor VII activation occurs postprandially. A proportion of activated factor VII (VIIa) circulates in complex with antithrombin (VIIaAT). Our primary objective was to assess the effects of postprandial lipemia on circulating VIIaAT, procoagulant phospholipid (PPL) activity, and thrombin generation.

METHODS

Plasma samples from postmyocardial infarction patients (n = 40) and controls (n = 39) were taken before and at 3 and 6 hours during a standardized oral fat tolerance test (OFTT). Fasting PPL activity measurements were also made in a second cohort of 108 postinfarction patients and 109 controls. VIIaAT was analyzed with the Asserachrom VIIaAT ELISA, PPL activity with the STA-Procoag-PPL kit, and thrombin generation with calibrated automated thrombogram with PRP-Reagent as trigger (all Diagnostica Stago products).

RESULTS

Postprandially, VIIaAT increased in all samples without significant case-control differences in the overall response during the OFTT. Thrombin generation measures peak height and velocity, and PPL activity, were marginally affected by the test meal in the controls. Levels of all patient baseline measures were significantly different from controls, indicating a more hypercoagulable state, and these differences were maintained throughout the OFTT. Fasting samples from cases showed higher PPL activity than control samples.

CONCLUSION

Viewing VIIaAT quantitation as a surrogate for TF activity measurement, postprandial increase in VIIaAT may reflect a mechanism that adds to the cardiovascular risk associated with postprandial lipemia. On the other hand, the impact of postprandial lipemia on PPL activity and thrombin generation seems to be minor.

Impact of metabolic syndrome on lipid target achievements in the Arabian Gulf: findings from the CEPHEUS study

BACKGROUND

The aim of this study was to determine the impact of metabolic syndrome (MetS) on lipid target achievements in the Arabian Gulf.

METHODS

The centralized pan-middle east survey on the undertreatment of hypercholesterolemia (CEPHEUS) included 4171 high and very high atherosclerotic cardiovascular disease (ASCVD) risk patients from six Arabian Gulf countries. Analyses were performed using univariate statistics.

RESULTS

The overall mean age was 57 ± 11 years, 41 % were females and 71 % had MetS. MetS patients were less likely to attain their HDL-C (34 vs. 79 %; P < 0.001), LDL-C (27 vs. 37 %; P < 0.001), non HDL-C (35 vs. 55 %; P < 0.001) and Apo B (35 vs. 54 %; P < 0.001) compared to those without MetS. Within the MetS cohort, those with very high ASCVD risk were less likely to attain their lipid targets compared to those with high ASCVD risk [HDL-C (32 vs. 41 %; P < 0.001), LDL-C (24 vs. 43 %; P < 0.001), non HDL-C (32 vs. 51 %; P < 0.001) and Apo B (33 vs. 40 %; P = 0.001)]. In those with MetS and very high ASCVD risk status, females were less likely to attain their HDL-C (27 vs. 36 %; P < 0.001), LDL-C (19 vs. 27 %; P < 0.001) and Apo B (30 vs. 35 %; P = 0.009) compared to males.

CONCLUSIONS

MetS was associated with low lipid therapeutic targets. Women and those with very high ASCVD risk were also less likely to attain their lipid targets in the Arabian Gulf.

Prepregnancy Adverse Lipid Profile and Subsequent Risk of Gestational Diabetes

CONTEXT

Lower low-density lipoprotein (LDL) peak diameter and a predominance of small, dense LDL are associated with type 2 diabetes, but it is unclear whether they are a risk factor for gestational diabetes mellitus (GDM).

OBJECTIVE

To evaluate whether prepregnancy lipid profile predicts the development of GDM during pregnancy.

DESIGN

A nested case-control study among women who participated in a multiphasic health exam, where blood was collected and stored between 1984 and 1996, and who then had a subsequent pregnancy between 1984 and 2009.

SETTING

Kaiser Permanente Northern California.

PARTICIPANTS

Cases were 254 women who developed GDM. Two controls were selected for each case and matched for year of blood draw, age at baseline, age at pregnancy, and number of intervening pregnancies.

MAIN OUTCOME MEASURES

Prepregnancy LDL peak diameter and prepregnancy lipid subfraction concentrations grouped according to size, and the odds of developing GDM.

RESULTS

Women in the lowest quartiles of LDL peak diameter and high-density lipoprotein had increased odds of GDM compared with women in the highest quartiles (odds ratio [95% CI], 2.60 [1.37-4.94] and 1.98 [1.01-3.86], respectively), in multivariable adjusted models. Being in the highest quartile of small and very small LDL subfractions also increased the odds of GDM (2.61 [1.35-5.03] and 2.44 [1.22-4.85], respectively).

CONCLUSIONS

Lower LDL peak diameter size and high-density lipoprotein levels and higher levels of small and very small LDL subfraction groups were present years before pregnancy in women who developed GDM. A prepregnancy atherogenic lipid profile may help identify women at risk of GDM to target for prevention.

Impact of age and menopausal status on the postprandial triacylglycerol response in healthy women

OBJECTIVE

To examine the impact of age and the natural menopause on the postprandial triacylglycerol (TAG) response in healthy women.

METHODS AND RESULTS

Thirty-seven premenopausal and sixty-one postmenopausal women underwent a sequential meal postprandial investigation, in which blood samples were taken at regular intervals after a test breakfast and lunch given at 0 and 330 min respectively. Lipids and glucose were measured in the fasting sample, with TAG analysed in the postprandial samples. Postmenopausal women were shown to have higher fasting total cholesterol, low density lipoprotein cholesterol (LDL-C) and glucose (P<0.02). Marked differences in the postprandial TAG response were evident between the groups, with a greater incremental area under the curve (IAUC) and maximum TAG concentration in the postmenopausal women (P<0.04). Multivariate regression analysis revealed both age and fasting TAG to be independently associated with the summary measures of the postprandial TAG response in the premenopausal women only. Interestingly, sub-division of the women into both younger and older pre- and postmenopausal subgroups, showed the most marked difference in TAG-IAUC to be between the younger and the older premenopausal women, whereas differences in fasting LDL-C were most evident between the older premenopausal and the younger postmenopausal women.

CONCLUSIONS

Our results suggest a divergence in the relationship of age and menopausal status with fasting LDL-C and postprandial TAG which may reflect differences in the metabolic effects of age and the menopause on these lipid risk markers or a greater impact of early oestrogen decline on pathways of TAG rather than LDL metabolism.

Novel aspects of postprandial lipemia in relation to atherosclerosis

Postprandial hyperlipidemia is considered to be a substantial risk factor for atherosclerosis. Interestingly, this concept has never been supported by randomized clinical trials. The difficulty lies in the fact that most interventions aimed to reduce postprandial lipemia, will also affect LDL-C levels. The atherogenic mechanisms of postprandial lipids and lipoproteins can be divided into direct lipoprotein-mediated and indirect effects; the latter, in part, by inducing an inflammatory state. Elevations in postprandial triglycerides (TG) have been related to the increased expression of postprandial leukocyte activation markers, up-regulation of pro-inflammatory genes in endothelial cells and involvement of the complement system. This set of events is part of the postprandial inflammatory response, which is one of the recently identified potential pro-atherogenic mechanisms of postprandial lipemia. Especially, complement component 3 levels show a close correlation with postprandial lipemia and are also important determinants of the metabolic syndrome. In clinical practice, fasting TG are frequently used as reflections of postprandial lipemia due to the close correlation between the two. The use of serial capillary measurements in an out-of-hospital situation is an alternative for oral fat loading tests. Daylong TG profiles reflect postprandial lipemia and are increased in conditions like the metabolic syndrome, type 2 diabetes and atherosclerosis. Studies are needed to elucidate the role of postprandial inflammation in atherogenesis and to find new methods in order to reduce selectively the postprandial inflammatory response. Future studies are needed to find new methods in order to reduce selectively the postprandial inflammatory response.

Impact of metformin versus the prandial insulin secretagogue, repaglinide, on fasting and postprandial glucose and lipid responses in non-obese patients with type 2 diabetes

OBJECTIVE

Non-obese patients with type 2 diabetes (T2DM) are characterized by predominant defective insulin secretion. However, in non-obese T2DM patients, metformin, targeting insulin resistance, is non-inferior to the prandial insulin secretagogue, repaglinide, controlling overall glycaemia (HbA1c). Whether the same apply for postprandial glucose and lipid metabolism is unknown. Here, we compared the effect of metformin versus repaglinide on postprandial metabolism in non-obese T2DM patients.

DESIGN

Single-centre, double-masked, double-dummy, crossover study during 2x4 months involving 96 non-obese (body mass index < or = 27 kg/m2) insulin-naïve T2DM patients. At enrolment, patients stopped prior oral hypoglycaemic agents therapies and after a 1-month run-in period on diet-only treatment, patients were randomized to repaglinide (2 mg) thrice daily followed by metformin (1 g) twice daily or vice versa each during 4 months with 1-month washout between interventions.

METHODS

Postprandial metabolism was evaluated by a standard test meal (3515 kJ; 54% fat, 13% protein and 33% carbohydrate) with blood sampling 0-6 h postprandially.

RESULTS

Fasting levels and total area under the curve (AUC) for plasma glucose, triglycerides and free fatty acids (FFA) changed equally between treatments. In contrast, fasting levels and AUC of total cholesterol, low-density lipoprotein (LDL) cholesterol, non-high-density lipoprotein (non-HDL) cholesterol and serum insulin were lower during metformin than repaglinide (mean (95% confidence intervals), LDL cholesterol difference metformin versus repaglinide: AUC: -0.17 mmol/l (-0.26; -0.08)). AUC differences remained significant after adjusting for fasting levels.

CONCLUSIONS

In non-obese T2DM patients, metformin reduced postprandial levels of glycaemia, triglycerides and FFA similarly compared to the prandial insulin secretagogue, repaglinide. Furthermore, metformin reduced fasting and postprandial cholesterolaemia and insulinaemia compared with repaglinide. These data support prescription of metformin as the preferred drug in non-obese patients with T2DM targeting fasting and postprandial glucose and lipid metabolism.

Dietary, physiological, genetic and pathological influences on postprandial lipid metabolism

Most of diurnal time is spent in a postprandial state due to successive meal intakes during the day. As long as the meals contain enough fat, a transient increase in triacylglycerolaemia and a change in lipoprotein pattern occurs. The extent and kinetics of such postprandial changes are highly variable and are modulated by numerous factors. This review focuses on factors affecting postprandial lipoprotein metabolism and genes, their variability and their relationship with intermediate phenotypes and risk of CHD. Postprandial lipoprotein metabolism is modulated by background dietary pattern as well as meal composition (fat amount and type, carbohydrate, protein, fibre, alcohol) and several lifestyle conditions (physical activity, tobacco use), physiological factors (age, gender, menopausal status) and pathological conditions (obesity, insulin resistance, diabetes mellitus). The roles of many genes have been explored in order to establish the possible implications of their variability in lipid metabolism and CHD risk. The postprandial lipid response has been shown to be modified by polymorphisms within the genes for apo A-I, A-IV, A-V, E, B, C-I and C-III, lipoprotein lipase, hepatic lipase, fatty acid binding and transport proteins, microsomal triglyceride transfer protein and scavenger receptor class B type I. Overall, the variability in postprandial response is important and complex, and the interactions between nutrients or dietary or meal compositions and gene variants need further investigation. The extent of present knowledge and needs for future studies are discussed in light of ongoing developments in nutrigenetics.

Effect of dietary cholesterol and fat on cell cholesterol transfer to postprandial plasma in hyperlipidemic men

Postprandial chylomicrons are potent ultimate acceptors of cell membrane cholesterol and are believed to accelerate reverse cholesterol transport (RCT). We compared the effects of meals rich in polyunsaturated fat (PUFA) and either high (605 mg) or low (151 mg) in cholesterol and a meal rich in dairy fat (DF) in the form of cream on net in vitro transport of red blood cell (RBC) membrane cholesterol to 4 and 6 h postprandial plasma in eight normotriglyceridemic (NTG-H) and eight hypertriglyceridemic (HTG-H) men with mild to moderate hypercholesterolemia. In HTG-H men, cell cholesterol accumulation in 6-h postprandial plasma was significantly (P = 0.02) less after the PUFA-HC meal compared with the other meals. The significant (P < 0.001) increase in cell plus endogenous cholesterol accumulation in the triglyceride-rich lipoprotein (TRL) fraction of 4 h postprandial plasma incubated with RBC was significantly (P = 0.007) higher after the PUFA-HC meal compared with DF meal in HTG-H men. In NTG-H men, cholesterol accumulation in plasma and plasma lipoproteins in the presence and absence of RBC was not significantly affected by the type of meal ingested. These data suggest that addition of large amounts of cholesterol to a PUFA meal may impair diffusion-mediated transport of cell membrane cholesterol to postprandial plasma and that replacing DF with PUFA in a meal increases postprandial lipemia and may potentially increase cholesterol accumulation in atherogenic postprandial TRL in HTG-H men.

Management of dyslipidemia in the metabolic syndrome: recommendations of the Spanish HDL-Forum

In order to characterize the metabolic syndrome it becomes necessary to establish a number of diagnostic criteria. Because of its impact on cardiovascular morbidity/mortality, considerable attention has been focussed on the dyslipidemia accompanying the metabolic syndrome. The aim of this review is to highlight the fundamental aspects of the pathophysiology, diagnosis, and the treatment of the metabolic syndrome dyslipidemia with recommendations to clinicians. The clinical expression of the metabolic syndrome dyslipidemia is characterized by hypertriglyceridemia and low levels of high-density lipoprotein-cholesterol (HDL-C). In addition, metabolic syndrome dyslipidemia is associated with high levels of apolipoprotein (apo) B-100-rich particles of a particularly atherogenic phenotype (small dense low-density lipoprotein-cholesterol [LDL-C]. High levels of triglyceride-rich particles (very low-density lipoprotein) are also evident both at baseline and in overload situations (postprandial hyperlipidemia). Overall, the 'quantitative' dyslipidemia characterized by hypertriglyceridemia and low levels of HDL-C and the 'qualitative' dyslipidemia characterized by high levels of apo B-100- and triglyceride-rich particles, together with insulin resistance, constitute an atherogenic triad in patients with the metabolic syndrome. The therapeutic management of the metabolic syndrome, regardless of the control of the bodyweight, BP, hyperglycemia or overt diabetes mellitus, aims at maintaining optimum plasma lipid levels. Therapeutic goals are similar to those for high-risk situations because of the coexistence of multiple risk factors. The primary goal in treatment should be achieving an LDL-C level of <100 mg/dL (or <70 mg/dL in cases with established ischemic heart disease or risk equivalents). A further goal is increasing the HDL-C level to >or=40 mg/dL in men or 50 mg/dL in women. A non-HDL-C goal of 130 mg/dL should also be aimed at in cases of hypertriglyceridemia. Lifestyle interventions, such as maintaining an adequate diet, and a physical activity program, constitute an essential part of management. Nevertheless, when pharmacologic therapy becomes necessary, fibrates and HMG-CoA reductase inhibitors (statins) are the most effective drugs in controlling the metabolic syndrome hyperlipidemia, and are thus the drugs of first choice. Fibrates are effective in lowering triglycerides and increasing HDL-C levels, the two most frequent abnormalities associated with the metabolic syndrome, and statins are effective in lowering LDL-C levels, even though hypercholesterolemia occurs less frequently. In addition, the combination of fibrates and statins is highly effective in controlling abnormalities of the lipid profile in patients with the metabolic syndrome.

Clinical importance and therapeutic modulation of small dense low-density lipoprotein particles

The National Cholesterol Education Programme Adult Treatment Panel III accepted the predominance of small dense low-density lipoprotein (sdLDL) as an emerging cardiovascular disease (CVD) risk factor. Most studies suggest that measuring low-density lipoprotein (LDL) particle size, sdLDL cholesterol content and LDL particle number provides additional assessment of CVD risk. Therapeutic modulation of small LDL size, number and distribution may decrease CVD risk; however, no definitive causal relationship is established, probably due to the close association between sdLDL and triglycerides and other risk factors (e.g., high-density lipoprotein, insulin resistance and diabetes). This review addresses the formation and measurement of sdLDL, as well as the relationship between sdLDL particles and CVD. The effect of hypolipidaemic (statins, fibrates and ezetimibe) and hypoglycaemic (glitazones) agents on LDL size and distribution is also discussed.

Postprandial, but not postabsorptive low-density lipoproteins increase the expression of intercellular adhesion molecule-1 in human aortic endothelial cells

The magnitude of postprandial lipemia has been identified as independent risk factor for the development of coronary artery disease. To test the effect of postprandial versus postabsorptive low-density lipoproteins (LDL) on the expression of adhesion molecules, LDL were isolated from healthy subjects before and 4h after ingestion of a standardized fatty test meal. We used flow cytometry and Northern blotting to quantify cell adhesion molecules in human aortic endothelial cells (HAEC). The adherence of leukocytes to HAEC was analyzed using a monocyte adhesion assay. Incubation of HAEC with postprandial, but not postabsorptive LDL induced a two-fold increase in the surface expression of intercellular adhesion molecule-1 (ICAM-1), but not of E-selectin or vascular cell adhesion molecule-1. In addition, increased amounts of ICAM-1 transcripts were found in HAEC treated with postprandial LDL. The adhesion of monocytes to HAEC was enhanced after pretreatment with postprandial, but not with postabsorptive LDL. We conclude that postprandial, but not postabsorptive LDL increase the surface expression of ICAM-1 in HAEC apparently by de novo protein synthesis leading to increased adhesion of monocytes. The upregulation of ICAM-1 by postprandial LDL may explain part of the proatherogenic effect of high postprandial lipemia.

Genotype of the mutant LDL receptor allele is associated with LDL particle size heterogeneity in familial hypercholesterolemia

Small, dense LDL particles have been associated with an increased risk of coronary artery disease. In order to assess the potential contribution of the genotype of the LDL receptor to LDL particle size heterogeneity in familial hypercholesterolemia (FH), we examined the electrophoretic characteristics of LDL particles in a large cohort of FH heterozygotes and controls. A total of 259 FH heterozygotes and 208 controls participated in the study. FH subjects were carriers of one of the nine French Canadian mutations in the LDL receptor gene. LDL particles were characterized by polyacrylamide gradient gel electrophoresis following a 6-week lipid-lowering drug-free baseline period. LDL-peak particle diameter (LDL-PPD), representing the most abundant LDL particle subpopulation, was significantly smaller in FH heterozygotes carrying a negative-receptor mutation than in subjects carrying a defective-receptor mutation (negative-receptor = 257.3 +/- 4.1 A versus defective-receptor = 259.0 +/- 4.3 A, p = 0.0006). No significant difference in plasma CETP concentrations was found between these two genotypic groups. Moreover, compared with controls having low triglyceride levels, negative-receptor subjects with high triglyceride levels had a relative risk of 19.6 (p < 0.0001) of having small, dense LDL particles while this risk was not significantly increased among defective-receptor subjects. Multivariate analysis showed that the LDL receptor status accounted for 5.7% of the variance in the LDL-PPD after adjustment for covariates. These results suggest that the genotype of the mutant LDL receptor allele was independently associated with variations in LDL-PPD and could partly explain why negative-receptor FH heterozygotes may be at greater risk of cardiovascular disease than defective-receptor FH subjects.

Association between LDL particle size and postprandial increase of remnant-like particles in Japanese type 2 diabetic patients

Small, dense LDL, as well as chylomicron- and VLDL-remnant lipoproteins, are known to be important risk factors for coronary heart disease in patients with type 2 diabetes mellitus. The aim of this study was to clarify the relationship between LDL particle size and postprandial remnant lipoprotein levels in Japanese type 2 diabetic patients. Forty-six patients with type 2 diabetes mellitus were divided into tertiles according to LDL particle size. The peak LDL particle diameter was <26.30 nm in tertile 1, 26.30-26.85 nm in tertile 2, and >26.85 nm in tertile 3. After a test meal, tertile 1 had a significantly greater increment of triglycerides (TG), remnant-like particle (RLP)-TG, and RLP-cholesterol (RLP-C) than tertiles 2 and 3. There was a negative correlation between LDL particle size and the postprandial increases of TG, RLP-TG, and RLP-C. These results indicate that smaller sized LDL particles may be a marker of fasting state for an exaggerated postprandial increase of remnant lipoproteins as well as an increase of TG-rich lipoproteins.

Relationship between low-density lipoprotein subclasses and asymptomatic atherosclerosis in subjects from the Atherosclerosis Risk in Communities (ARIC) Study

Low-density lipoprotein (LDL) particle size has been associated with coronary heart disease, but an association between LDL size and preclinical atherosclerosis is less well established. Using gradient gel electrophoresis, large (A), intermediate (I) and small (B) LDL size subclasses were determined in 198 cases with asymptomatic carotid artery atherosclerosis (determined by B-mode ultrasonography) and 318 controls from the Atherosclerosis Risk in Communities (ARIC) Study. In Caucasians, a smaller LDL size was more prevalent in men and associated with a higher body mass index, hypertension prevalence, and plasma total- and LDL-cholesterol and triglycerides, but lower HDL-cholesterol. In African-Americans, a smaller LDL size was associated with higher triglycerides and lower HDL-cholesterol and hypertension prevalence. In Caucasians, Subclass B prevalence was 29.1% among cases and 14.8% among controls. The odds ratio (95% confidence interval) for Subclass B rather than Subclass A in Caucasian cases was 2.94 (1.67-5.17); the association remained significant after controlling for age, body mass index, smoking, and either plasma triglycerides or HDL-cholesterol. In African-Americans, however, there was no significant association between LDL subclass and case status. A predominance of smaller LDL particles is associated with asymptomatic carotid artery atherosclerosis in Caucasians, through mechanisms that remain to be elucidated.

The -1131T-->C polymorphism in the apolipoprotein A5 gene is associated with postprandial hypertriacylglycerolemia; elevated small, dense LDL concentrations; and oxidative stress in nonobese Korean men

BACKGROUND

Apolipoprotein A5 plays an important role in modulating triacylglycerol metabolism in experimental animal models.

OBJECTIVE

The objective was to determine associations of the common apolipoprotein A5 gene (APOA5) -1131T-->C polymorphism with postprandial lipemic response and other cardiovascular disease risk factors in humans.

DESIGN

Healthy, nonobese subjects [n = 158; mean (+/-SEM) age: 33.8 +/- 1.2 y; body mass index (in kg/m(2)): 23.3 +/- 0.3] were subdivided into 3 genotype groups: TT (n = 85), TC (n = 56), and CC (n = 17). We measured fasting and postprandial lipid concentrations, lipid peroxidation, C-reactive protein concentrations, and DNA damage.

RESULTS

Fasting triacylglycerol concentrations in carriers of the C allele were higher (P < 0.05) than in carriers of the TT genotype. No other significant genotype-related differences were observed for any of the other baseline measures. After consumption of a mixed meal, carriers of the C allele had significantly greater increases in total chylomicron and VLDL triacylglycerol than did subjects with the TT genotype. Moreover, carriers of the C allele had higher dense LDL, serum C-reactive protein, and urinary 8-epi-prostaglandin F(2alpha) concentrations and more lymphocyte DNA damage. Conversely, we did not find significant genotype-related differences in postprandial glucose, insulin, or free fatty acid measures.

CONCLUSIONS

Our data confirm the genetic modulation of serum fasting triacylglycerol concentrations by the APOA5 gene polymorphism and extend this observation to postprandial triacylglycerol concentrations and to markers of oxidation and inflammation. The presence of the C allele in the APOA5 promoter region at position 1131 could be a significant factor contributing to higher cardiovascular disease risk in Koreans independently of common environmental factors.

Gender influence on plasma triacylglycerol response to meals with different monounsaturated and saturated fatty acid content

OBJECTIVE

Both gender and meal fatty acid composition modulate postprandial triacylglycerol (TAG) metabolism, but little information exists on their interaction. We compared postprandial TAG concentrations in men and women after test meals differing in the proportion of monounsaturated (MUFA) and saturated fatty acids (SFA).

SUBJECTS

Nine men (body mass index, BMI: 24.5+/-2.3 kg/m(2)) (mean+/-s.d.) and 10 premenopausal women (BMI: 21.2+/-1.7 kg/m(2)), young and healthy, habituated to a relatively high MUFA diet.

DESIGN

Plasma responses were studied after subjects consumed two meals, each providing 60 g of fat and 4.7 MJ, on different occasions: one meal was rich in MUFA (MUFA meal: 40 g MUFA; 12 g SFA) and the other meal was rich in SFA (SFA meal: 20 g MUFA; 32 g SFA). The total body and abdominal fat mass were assessed by dual energy X-ray absorptiometry.

RESULTS

Fasting plasma TAG concentration did not differ between meals or genders. No gender differences were observed in either total body or abdominal fat mass. The area under the plasma concentration vs time curve was on average 60% higher (P<0.001) in men than women. Repeated measures ANOVA showed a significant effect of meal x time interaction in men (P<0.001) but not in women (P=0.84). In men, maximal plasma TAG occurred at 4 h and was significantly greater after the MUFA meal (2.10+/-0.20 mmol/l) (mean+/-s.e.m.) than after the SFA meal (1.66+/-0.19 mmol/l) (P=0.01). TAG concentration at 5 h was also significantly greater after the MUFA meal. In women, the patterns of TAG responses were identical after the MUFA and SFA meals.

CONCLUSIONS

This study provides evidence that gender influences postprandial TAG concentrations when meal fatty acid composition is altered.

Relationship between cholesteryl ester transfer protein and LDL heterogeneity in familial hypercholesterolemia

Small, dense LDL particles have been associated with an increased risk of coronary artery disease, and cholesteryl ester transfer protein (CETP) has been suggested to play a role in LDL particle remodeling. We examined the relationship between LDL heterogeneity and plasma CETP mass in familial hypercholesterolemia (FH). LDL particles were characterized by polyacrylamide gradient gel electrophoresis in a total of 259 FH heterozygotes and 208 nonFH controls. CETP mass was measured by enzyme-linked immunosorbent assay in a subgroup of 240 participants, which included 120 FH patients matched with 120 controls. As compared with controls, FH subjects had an 11% higher CETP mass. Moreover, LDL-peak particle diameter (LDL-PPD) was significantly smaller in FH heterozygotes than in controls (258.1 +/- 4.8 vs. 259.2 +/- 4.1 A; P = 0.01) after adjustment for covariates. There was also an inverse relationship between LDL-PPD and CETP mass (R = -0.15; P = 0.02), and this relationship was abolished by adjustment for the FH/control status, indicating that LDL-PPD changes in FH are mediated, at least in part, by an increase in plasma CETP mass concentrations. These results suggest that increased plasma CETP mass concentrations could lead to significant LDL particle remodeling in FH heterozygotes and could contribute to the pathogenesis of atherosclerosis.

Metabolic abnormalities: triglyceride and low-density lipoprotein

Increased plasma triglyceride and reduced high-density lipoprotein cholesterol are key features of the metabolic syndrome. Although elevated low-density lipoprotein cholesterol is not an integral characteristic of this syndrome, there is commonly an increase in the proportion of small, dense low-density lipoprotein particles. Together, these abnormalities constitute the atherogenic dyslipidemia of the metabolic syndrome. This article reviews the pathophysiology of altered triglyceride and low-density lipoprotein metabolism in the metabolic syndrome, outlines the relationship of these lipoprotein abnormalities to increased risk of coronary heart disease,and highlights the application of this information to clinical practice. The role of reduced high-density lipoprotein in the metabolic syndrome is discussed elsewhere in this issue.

Postprandial lipemia and cardiovascular disease

Postprandial lipemia, characterized by a rise in triglyceride-rich lipoproteins after eating, is a dynamic, nonsteady-state condition in which humans spend the majority of time. There are several lines of evidence suggesting that postprandial lipemia increases risk of atherogenesis. Clinical data show a correlation between postprandial lipoproteins and the presence/progression of coronary artery disease and carotid intimal thickness. Mechanistic studies demonstrate that triglyceride-rich lipoprotein remnants may have adverse effects on endothelium and can penetrate into the subendothelial space. Exchange of core lipids between postprandial lipoproteins and low-density lipoprotein (LDL)/high-density lipoprotein (HDL) is increased during prolonged lipemia, resulting in small, dense LDL particles and reduced HDL cholesterol levels. Hemostatic variables, including clotting factors, platelet reactivity, and monocyte cytokine expression, may be increased during postprandial lipemia. Collectively, these data suggest that assessment and treatment of atherosclerosis should include parameters related to postprandial lipemia.

Impact of postprandial variation in triglyceridemia on low-density lipoprotein particle size

The fasting atherogenic dyslipidemia of visceral obesity, which includes the presence of small, dense low-density lipoprotein (LDL) particles, is predictive of an increased risk of coronary heart disease (CHD). It has also been suggested that progression of atherosclerosis may be accelerated in the presence of postprandial hyperlipidemia independently from the fasting dyslipidemic state. Studies have shown that the best predictor of postprandial hyperlipidemia and of the small, dense LDL phenotype is fasting triglyceride (TG) concentration. In the present study, we evaluated the impact of postprandial hypertriglyceridemia on the variation in LDL particle size. Fasting (0 hour) and postprandial changes (2, 4, 6, and 8 hours) in LDL particle size were measured by nondenaturing 2% to 16% polyacrylamide gel electrophoresis in a sample of 49 men (mean age +/- SD: 46.6 +/- 9.2 years) who underwent a standardized breakfast with a high-fat (64% calories as fat) content. The postprandial increase in TG levels was associated with a transient reduction in LDL particle size, the most substantial reduction being observed 4 hours (-1.0 +/- 2.4 A) after the oral fat load. Although there were strong correlations between TG-rich lipoprotein (TRL)-TG levels and LDL particle size in the fasting state (r=-0.71, P<.0001) as well as 4 hours after the oral fat load (r=-0.70, P<.0001), changes in TRL-TG concentrations during the postprandial state (from time 0 to 4 hours) were not associated with changes in LDL particle size during this period (r=-0.04, not significant [NS]). However, among subgroups of men matched for similar fasting TRL-TG levels (n=12), subjects with the highest total area under the curve (AUC) of TRL-TG after the fat load were characterized by smaller LDL particle size at 6 and 8 hours compared with men with the lowest AUC TRL-TG (P<.02). Men displaying the highest postprandial AUC TRL-TG were also characterized by the greatest accumulation of visceral adipose tissue (AT) (P<.05). These results indicate that the hypertriglyceridemic (hyperTG) state induced by a high-fat meal is associated with a transient reduction in LDL peak particle diameter, which is not proportionate, however, to the level of TG achieved in the postprandial state. Furthermore, despite similar TG levels at baseline, viscerally obese men with an impaired postprandial lipemia had smaller LDL particles at the end of the oral fat load than obese men with a lower accumulation of visceral AT.

Intimal retention of cholesterol derived from apolipoprotein B100- and apolipoprotein B48-containing lipoproteins in carotid arteries of Watanabe heritable hyperlipidemic rabbits

OBJECTIVE

The arterial retention of apolipoprotein (apo) B100- and apoB48-containing lipoproteins was simultaneously determined in a rabbit model of human hypercholesterolemia using 3D confocal microscopy.

METHODS AND RESULTS

Lipoproteins containing apoB100 (LDL) and apoB48 (chylomicron remnants) were differentially conjugated with fluorophores and simultaneously perfused at equivalent concentrations under physiological conditions in situ through carotid vessels of Watanabe heritable hyperlipidemic rabbits and compared with controls. Retention of lipoproteins was defined as the amount remaining after an extensive washout phase. LDL and chylomicron remnants were both retained, primarily within the subendothelial space. Without a concomitant increase in exposure to lipoproteins, we found a marked increase in the retention of cholesterol within the intima of Watanabe heritable hyperlipidemic rabbits compared with controls, specifically because of increased entrapment of apoB48-containing lipoproteins.

CONCLUSIONS

Collectively, our data suggest that hypercholesterolemia induced as a consequence of LDL receptor deficiency differentially influences retention of LDL and of chylomicron remnants.

In vitro and in vivo lipolysis of plasma triglycerides increases the resistance to oxidative modification of low-density lipoproteins

BACKGROUND

The majority of studies on low-density lipoprotein (LDL) particle size and susceptibility to oxidative modification have been either descriptive or interventional, but there are few mechanistic studies.

MATERIALS AND METHODS

Effects of exhaustive in vitro and in vivo lipolysis of serum and plasma triglycerides, respectively, by lipoprotein lipase (LPL) were investigated in healthy normotriglyceridemic men. The LDL end-product of lipolysis of very low-density lipoprotein (VLDL) underwent compositional analysis, gradient gel electrophoresis and an assessment of resistance to copper-induced oxidative modification.

RESULTS

The LDL particle contents of free fatty acid and alpha-tocopherol increased, whereas the contents of free and esterified cholesterol, alpha-carotene and coenzyme Q10 decreased upon incubation of serum with LPL in vitro. The LDL particle size decreased and the resistance to the oxidative modification of LDL increased. Lipolysis of plasma triglycerides in vivo, achieved by intravenous injection of heparin, did not alter the LDL particle size but increased the resistance to the oxidative modification of LDL. This change was accompanied by an increase in the LDL particle content of alpha-tocopherol, whereas the free fatty acid content was unaltered.

CONCLUSIONS

The results show that the increased resistance to oxidative modification of LDL after lipolysis of plasma triglycerides was concomitant with an increased LDL particle content of alpha-tocopherol, and that free fatty acids did not seem to contribute to the increased resistance to oxidative modification of LDL in vivo. Furthermore, our data indicate that the resistance of LDL to oxidative modification is not dependent on particle size.

Metabolic origins and clinical significance of LDL heterogeneity

LDLs in humans comprise multiple distinct subspecies that differ in their metabolic behavior and pathologic roles. Metabolic turnover studies suggest that this heterogeneity results from multiple pathways, including catabolism of different VLDL and IDL precursors, metabolic remodeling, and direct production. A common lipoprotein profile designated atherogenic lipoprotein phenotype is characterized by a predominance of small dense LDL particles. Multiple features of this phenotype, including increased levels of triglyceride rich lipoprotein remnants and IDLs, reduced levels of HDL and an association with insulin resistance, contribute to increased risk for coronary heart disease compared with individuals with a predominance of larger LDL. Increased atherogenic potential of small dense LDL is suggested by greater propensity for transport into the subendothelial space, increased binding to arterial proteoglycans, and susceptibility to oxidative modification. Large LDL particles also can be associated with increased coronary disease risk, particularly in the setting of normal or low triglyceride levels. Like small LDL, large LDL exhibits reduced LDL receptor affinity compared with intermediate sized LDL. Future delineation of the determinants of heterogeneity of LDL and other apoB-containing lipoproteins may contribute to improved identification and management of patients at high risk for atherosclerotic disease.

Changes in LDL particle composition after the consumption of meals containing different amounts and types of fat

BACKGROUND

Remodeling of lipoprotein particles in the postprandial period is considered to be an important source of atherogenic particles, but acute changes occurring after meals have been little studied.

OBJECTIVE

We sought to characterize changes in LDL particle composition occurring after a single meal, with particular reference to potential lipid exchange with particles carrying dietary fatty acids.

DESIGN

In a balanced design, 8 healthy subjects ingested isoenergetic meals of different fat content: low-fat, rich in saturated fatty acids (SFAs), and rich in polyunsaturated fatty acids (PUFAs). We investigated changes in LDL composition 4 and 6 h after meal ingestion.

RESULTS

The LDL triacylglycerol-to-protein ratio closely mirrored the plasma triacylglycerol concentrations after each of the meals, and there was a strong association between these variables in both the fasting and postprandial states (P < 0.001). A postprandial increase in LDL triacylglycerol was associated with a decrease in LDL cholesterol. There were no effects of the ingestion of a single meal on the LDL density profiles for protein or for any of the lipid components. The fatty acid composition of total LDL lipids changed in the postprandial period, with an enrichment in PUFA after the PUFA-rich meal and in SFA after the SFA-rich meal.

CONCLUSIONS

The changes observed in LDL composition after single meals are in accord with the proposition that there is neutral lipid exchange in the postprandial period, with triacylglycerol enrichment of LDL particles at the expense of cholesteryl esters. The change in the fatty acid composition of LDL particles implies significant lipid exchange with particles containing dietary fat.

Postprandial lipemia--effect of lipid-lowering drugs

Exaggerated postprandial hyperlipidemia has been associated with cardiovascular disease. The mechanisms underlying this association are likely to depend on a multitude of effects. Potentially atherogenic remnants of triglyceride-rich lipoproteins (TRL) accumulate in the postprandial state. In addition, TRL may promote the formation of small dense LDL. There are some indications that the postprandial period is a hypercoagulable state and endothelial function seems to be hampered after acute fat intake. Conventional lipid lowering drugs such as statins and fibrates have the potency of reducing postprandial hyperlipidemia, but the fibrates seem to be more effective in this respect. There is a complete lack of prospective studies linking inefficient postprandial lipid metabolism with clinical endpoints and there is also a need to include investigations of postprandial lipid metabolism in the evaluation of novel drugs affecting lipid metabolism and insulin resistance.

Contribution of hepatic lipase, lipoprotein lipase, and cholesteryl ester transfer protein to LDL and HDL heterogeneity in healthy women

Hepatic lipase (HL) and cholesteryl ester transfer protein (CETP) have been independently associated with low density lipoprotein (LDL) and high density lipoprotein (HDL) size in different cohorts. These studies have been conducted mainly in men and in subjects with dyslipidemia. Ours is a comprehensive study of the proposed biochemical determinants (lipoprotein lipase, HL, CETP, and triglycerides) and genetic determinants (HL gene [LIPC] and Taq1B) of small dense LDL (sdLDL) and HDL subspecies in a large cohort of 120 normolipidemic, nondiabetic, premenopausal women. HL (P<0.001) and lipoprotein lipase activities (P=0.006) were independently associated with LDL buoyancy, whereas CETP (P=0.76) and triglycerides (P=0.06) were not. The women with more sdLDL had higher HL activity (P=0.007), lower HDL2 cholesterol (P<0.001), and lower frequency of the HL (LIPC) T allele (P=0.034) than did the women with buoyant LDL. The LIPC variant was associated with HL activity (P<0.001), HDL2 cholesterol (P=0.034), and LDL buoyancy (P=0.03), whereas the Taq1B polymorphism in the CETP gene was associated with CETP mass (P=0.002) and HDL3 cholesterol (P=0.039). These results suggest that HL activity and HL gene promoter polymorphism play a significant role in determining LDL and HDL heterogeneity in healthy women without hypertriglyceridemia. Thus, HL is an important determinant of sdLDL and HDL2 cholesterol in normal physiological states as well as in the pathogenesis of various disease processes.

Postprandial triglyceride-rich lipoprotein metabolism and insulin sensitivity in nonalcoholic steatohepatitis patients

Nonalcoholic steatohepatitis (NASH) is a syndrome frequently associated with obesity, diabetes mellitus, and dyslipidemia. Increased fasting insulinemia and blood glucose levels may trigger a reduced catabolism of lipoproteins rich in triglycerides by lipoprotein lipase (LPL) and an increase in their fasting and postprandial levels. An association between postprandial lipemia and coronary heart disease has been observed, and many studies now support this concept. The most important result of our study is the increase in triglyceride-rich lipoproteins response after a fat load in NASH patients, the increase of incremental area under the postprandial curve, and the duration of the hypertriglyceridemic peaks. The persisting postprandial plasma triglyceride elevation in NASH patients was mostly due to the elevated plasma level of large triglyceride-rich particles. These data are coupled with lower plasma HDL2-cholesterol levels. As for lipoprotein analyses, the number of apolipoprotein B100 (ApoB100) particles is not significantly different between the two groups, and the higher content of triglycerides in NASH very low density lipoproteins (VLDL) increases the triglyceride-to-ApoB ratio and the particle size. A decreased enzymatic activity of LPL or a defective assembly and secretion of VLDL from hepatocytes due to a moderate reduction in microsomal triglyceride transfer protein could be involved in the overloading of VLDL. Moreover, the undetectable levels of ApoB48 in triglyceride-rich lipoproteins fraction A could be related to the synthesis of smaller and denser chylomicrons. NASH patients not only are insulin resistant but also tend to present alterations in fatty meal delivery, suggesting that an increase in fasting plasma insulin and glucose, with insulin resistance, joins with depressed metabolism of triglyceride-rich lipoproteins. An increase in postprandial triglyceride levels with production of large VLDL suggests an atherogenic behavior of lipid metabolism, in accordance with the high prevalence of the metabolic syndrome in NASH patients. This paper suggests that a fat load may be useful in early detection of atherogenic risk in the presence of otherwise normal fasting plasma lipids.

Effects of different nutrient intakes on daytime triacylglycerolemia in healthy, normolipemic, free-living men

BACKGROUND

Postprandial studies with standardized mixed meals have shown that ingestion of high-carbohydrate diets is associated with elevated plasma triacylglycerol (TG) concentrations.

OBJECTIVE

We evaluated the effects of different nutritional components on daytime triacylglycerolemia in 58 healthy, free-living, normolipemic men.

DESIGN

Capillary TG (TGc) was self-measured at 6 fixed time points over 3 d. Daytime TGc profiles were calculated as areas under the curve (AUCs) for absolute and incremental changes in TGc concentrations (TGc-AUC and DeltaTGc-AUC, respectively). Food intake was recorded in a diary.

RESULTS

The mean (+/-SD) fasting TGc concentration, TGc-AUC, and DeltaTGc-AUC were 1.20 +/- 0.41 mmol/L, 24.1 +/- 6.9 mmol x h/L, and 7.3 +/- 4.5 mmol x h/L, respectively. Mean total energy intake was 10881 +/- 2536 kJ/d. Total intakes of fat, carbohydrate, and protein were 95 +/- 25 (33% of energy), 304 +/- 69 (48% of energy), and 101 +/- 27 (16% of energy) g/d, respectively. Fasting TGc concentrations and TGc-AUC were not related to dietary intake. The mean DeltaTGc-AUC was significantly related to total carbohydrate (r = 0.38, P < 0.005), protein (r = 0.29, P < 0.05), and energy (r = 0.28, P < 0.05) intakes. Fat intake (as a % of energy) was negatively associated with the mean DeltaTGc-AUC (r = -0.30, P < 0.05). When the study group was subdivided into tertiles on the basis of fat intake (27.2%, 33.5%, and 39.1% of energy, respectively), carbohydrate intake was 50.9%, 48.1%, and 44.6% of energy, respectively. DeltaTGc-AUC was significantly lower at the highest tertile of fat intake (4.8 +/- 4.3 mmol x h/L) than at the lowest (8.2 +/- 4.0 mmol x h/L) and intermediate (8.9 +/- 4.3 mmol x h/L) tertiles (P < 0.05 for each).

CONCLUSION

DeltaTGc-AUC is associated with the carbohydrate content of the diet in free-living men.

Exercise prevents the augmentation of postprandial lipaemia attributable to a low-fat high-carbohydrate diet

There is concern that replacement of dietary fat with carbohydrate may not reduce the overall risk of CHD because this replacement strategy elevates postprandial plasma triacylglycerol (TAG) concentrations. The present study was designed to test the hypothesis that daily exercise can offset the augmented postprandial lipaemia associated with a short-term high-carbohydrate diet. Nine healthy, normolipidaemic men aged 33 (sd 4) years consumed a test meal (g/kg body mass; 1.2 fat, 1.1 carbohydrate, 0.2 protein) on three occasions: after 3 d on a typical Western diet (46, 38 and 16 % energy from carbohydrate, fat and protein respectively); after 3 d on an isoenergetic high-carbohydrate diet (corresponding values: 70, 15 and 15 % energy); after 3 d on the same high-carbohydrate diet with 30 min moderate exercise daily. Fasting plasma TAG concentration was higher after the high-carbohydrate diet (1.15 (se 0.16) mmol/l) than after the Western diet (0.83 (se 0.10) mmol/l; ). Similarly, postprandial lipaemia (6 h total area under plasma TAG concentration v. time curve) was higher after the high-carbohydrate diet (12.54 (se 2.07) mmol/l.h) than after the Western diet (9.30 (se 1.30) mmol/l.h; ). The addition of exercise to the high-carbohydrate diet significantly reduced postprandial lipaemia (9.95 (se 1.94) mmol/l.h; when compared with the high-carbohydrate diet) but not fasting TAG concentration (1.02 (se 0.24) mmol/l). In conclusion, daily exercise prevented the augmentation of postprandial lipaemia attributable to the short-term high-carbohydrate diet and, thus, exercise may be a powerful adjunct to dietary change.

DIETARY ANDGENETICEFFECTS ONLOW-DENSITYLIPOPROTEINHETEROGENEITY

We have tested whether differences in distribution and dietary responsiveness of low-density lipoprotein (LDL) subclasses contribute to the variability in the magnitude of LDL-cholesterol reduction induced by diets low in total and saturated fat and high in carbohydrate. Our studies have focused on a common, genetically influenced metabolic profile, characterized by a predominance of small, dense LDL particles (subclass pattern B), that is associated with a two- to threefold increase in risk for coronary artery disease. We have found that healthy normolipidemic individuals with this trait show a greater reduction in LDL cholesterol and particle number in response to low-fat, high-carbohydrate diets than do unaffected individuals (subclass pattern A). Moreover, such diets result in reduced LDL particle size, with induction of pattern B in a substantial proportion of pattern A men. Recent studies have indicated that this response is under genetic influence. Future identification of the specific genes involved may lead to improved targeting of dietary therapies aimed at reducing cardiovascular disease risk.

Effects of atorvastatin versus fenofibrate on lipoprotein profiles, low-density lipoprotein subfraction distribution, and hemorheologic parameters in type 2 diabetes mellitus with mixed hyperlipoproteinemia

Diabetic dyslipoproteinemia characterized by hypertriglyceridemia, low high-density lipoprotein (HDL) cholesterol, and often elevated low-density lipoprotein (LDL) cholesterol with predominance of small, dense LDL is a strong risk factor for atherosclerosis. It is unclear whether fibrate or statin therapy is more effective in these patients. We compared atorvastatin (10 mg/day) with fenofibrate (200 mg/day), each for 6 weeks separated by a 6-week washout period in 13 patients (5 men and 8 women; mean age 60.0+/-6.8 years; body mass index 30.0+/-3.0 kg/m2) with type 2 diabetes mellitus (hemoglobin A1c 7.3+/-1.1%) and mixed hyperlipoproteinemia (LDL cholesterol 164.0+/-37.8 mg/dl, triglycerides 259.7+/-107 mg/dl, HDL cholesterol 48.7+/-11.0 mg/dl) using a randomized, crossover design. Lipid profiles, LDL subfraction distribution, fasting plasma viscosity, red cell aggregation, and fibrinogen concentrations were determined before and after each drug. Atorvastatin decreased all LDL subfractions (LDL cholesterol, -29%; p <0.01) including small, dense LDL. Fenofibrate predominantly decreased triglyceride concentrations (triglycerides, -39%; p <0.005) and induced a shift in LDL subtype distribution from small, dense LDL (-31%) to intermediate-dense LDL (+36%). The concentration of small, dense LDL was comparable during therapy to both drugs (atorvastatin 62.8+/-19.5 mg/dl, fenofibrate 63.0+/-18.1 mg/dl). Both drugs induced an increase in HDL cholesterol (atorvastatin +10%, p <0.05; fenofibrate +11%, p = 0.06). In addition, fenofibrate decreased fibrinogen concentration (-15%, p <0.01) associated with a decrease in plasma viscosity by 3% (p <0.01) and improved red cell aggregation by 15% (p <0.05), whereas atorvastatin did not affect any hemorheologic parameter. We conclude that atorvastatin and fenofibrate can improve lipoprotein metabolism in type 2 diabetes. However, the medications affect different aspects of lipoprotein metabolism.

The small, dense LDL phenotype as a correlate of postprandial lipemia in men

The atherogenic dyslipidemia of the insulin resistance syndrome is characterized by hypertriglyceridemia (hyperTG), elevated apolipoprotein (apo) B levels, reduced high-density lipoprotein (HDL) cholesterol concentrations and by an increased proportion of small, dense low-density lipoprotein (LDL) particles. Although the hyperTG-low HDL cholesterol dyslipidemia has been associated with an impaired clearance of dietary fat, the contribution of the small, dense LDL phenotype as an independent predictor of postprandial triglyceride (TG) clearance remains uncertain. We have therefore compared the postprandial TG response among three subgroups of men characterized by small, intermediate or large LDL particles in a total sample of 69 men (mean age +/- SD; 45.1 +/- 10.5 years). To identify men with small versus large LDL particles, the first (LDL peak particle diameter < 251.9 A) and the third (> 257.6 A) tertiles of the distribution of LDL particle diameters were used as cutoff points. Men with small, dense LDL particles had the expected fasting dyslipidemic profile (high TG-low HDL cholesterol levels) compared to men with large, buoyant LDL particles. The oral lipid tolerance test revealed that men with small, dense LDL particles had significantly higher total-, large-, and medium-TG-rich lipoprotein (TRL) responses to a fatty meal than men with large LDL particles (P < 0.03). In addition, within a subgroup of normolipidemic men (TG < 2.3 mmol/l and HDL cholesterol > 0.9 mmol/l), those with small, dense LDL particles had higher levels of total-, medium- and small-TRL responses compared to men with large, buoyant LDL particles (P < 0.05). Moreover, normotriglyceridemic men with small, dense LDL had higher levels of small-TRLs measured 8 h after the ingestion of the fat meal (P < 0.05) compared to normolipidemic men with large, buoyant LDL particles. Results of the present study suggest that the dense LDL phenotype may be an additional fasting marker of an exaggerated postprandial TG response and of an impaired clearance of TRLs.

Hypotriglyceridemic effect of Anka (a fermented rice product of monascus sp.) in rats

Experimental rats with hypertriglyceridemia were prepared by feeding a high-fructose diet. Dried Anka powder (2%), a rice product fermented with Monascus sp., was mixed with basic high-fructose (30%) or basal-diet feed. Serum and liver lipids were measured after 6 months. The concentrations of serum triglycerides, total cholesterol, VLDL-C, and LDL-C had significantly decreased, whereas that of HDL-C had slightly increased in 30% fructose-Anka-fed rats as compared with the 30% fructose-fed rats, but hepatic lipase activity had increased in the Anka-fed groups. The ratio of lipoprotein lipase/hepatic lipase was not significantly different between 30% fructose-Anka-fed rats and 30% fructose-fed rats. The dietary intake and weight of these two groups were approximately the same. Similar results were obtained in noninduced hypertriglyceridemic rats. The concentrations of triglycerides and cholesterol did not significantly differ in the liver. Interestingly, Anka can suppress serum triglycerides in rats with induced hypertriglyceridemia. The antioxidant enzyme SOD activity was also measured in serum, and no significant change was observed. On the basis of these findings, we suggest that Anka may be used to suppress hypertriglyceridemia and hyperlipidemia in rats and possibly in man.

ApoE polymorphism and fish oil supplementation in subjects with an atherogenic lipoprotein phenotype

The study assessed the efficacy of fish oil supplementation in counteracting the classic dyslipidemia of the atherogenic lipoprotein phenotype (ALP). In addition, the impact of the common apolipoprotein E (apoE) polymorphism on the fasting and postprandial lipid profile and on responsiveness to the dietary intervention was established. Fifty-five ALP males (aged 34 to 69 years, body mass index 22 to 35 kg/m(2), triglyceride [TG] levels 1.5 to 4.0 mmol/L, high density lipoprotein cholesterol [HDL-C] <1.1 mmol/l, and percent low density lipoprotein [LDL]-3 >40% total LDL) completed a randomized placebo-controlled crossover trial of fish oil (3.0 g eicosapentaenoic acid/docosahexaenoic acid per day) and placebo (olive oil) capsules with the 6-week treatment arms separated by a 12-week washout period. In addition to fasting blood samples, at the end of each intervention arm, a postprandial assessment of lipid metabolism was carried out. Fish oil supplementation resulted in a reduction in fasting TG level of 35% (P<0.001), in postprandial TG response of 26% (TG area under the curve, P<0.001), and in percent LDL-3 of 26% (P<0.05). However, no change in HDL-C levels was evident (P=0.752). ANCOVA showed that baseline HDL-C levels were significantly lower in apoE4 carriers (P=0.035). The apoE genotype also had a striking impact on lipid responses to fish oil intervention. Individuals with an apoE2 allele displayed a marked reduction in postprandial incremental TG response (TG incremental area under the curve, P=0.023) and a trend toward an increase in lipoprotein lipase activity relative to non-E2 carriers. In apoE4 individuals, a significant increase in total cholesterol and a trend toward a reduction in HDL-C relative to the common homozygous E3/E3 profile was evident. Our data demonstrate the efficacy of fish oil fatty acids in counteracting the proatherogenic lipid profile of the ALP but also that the apoE genotype influences responsiveness to this dietary treatment.

Effect of long-chain n-3 polyunsaturated fatty acids on fasting and postprandial triacylglycerol metabolism

Elevated plasma triacylglycerol concentrations have been associated with increased risk of coronary heart disease (CHD). In the past, the epidemiologic evidence about the causal role of triacylglycerols in CHD has not been well regarded, but recent prospective evidence shows that nonfasting plasma triacylglycerol concentration is a strong and independent predictor of future myocardial infarction. Elevated plasma triacylglycerol concentrations are associated with other CHD risk factors, namely reduced HDL-cholesterol concentrations and a preponderance of highly atherogenic, small, dense LDL particles. Plasma triacylglycerol concentrations increase after the ingestion of a fat-containing meal, and elevated postprandial triacylglycerolemia leads to a series of metabolic reactions that reduce HDL-cholesterol concentrations and promote the formation of small, dense LDL particles. The magnitude of the postprandial response is largely determined by fasting plasma triacylglycerol concentrations. Metabolism of plasma triacylglycerols also influences postprandial factor VII activation and the postprandial lipemic responsiveness to dietary cholesterol. Therefore, dietary factors that improve fasting plasma triacylglycerol concentrations must have a role in a healthy diet. Eicosapentaenoic and docosahexaenoic acids are n-3 polyunsaturated fatty acids (PUFAs) in fish oil that effectively reduce plasma triacylglycerol concentrations. Because n-3 PUFAs are effective at low doses (1 g n-3 PUFA/d), they provide a realistic option for the optimization of plasma triacylglycerol metabolism.

Net mass transfer of plasma cholesteryl esters and lipid transfer proteins in normolipidemic patients with peripheral vascular disease

The role of plasma cholesteryl ester transfer and lipid transfer proteins in atherosclerosis is unclear. Recent data suggest both antiatherogenic and atherogenic properties for cholesteryl ester transfer protein (CETP). The overall effect of CETP on atherosclerosis may thus vary depending on individual lipid metabolism. To test whether lipid transfer parameters are of importance even in patients without major lipid risk factors for atherosclerosis, CETP mass and activity, net mass transfer of cholesteryl esters between endogenous lipoproteins (CET), and phospholipid transfer protein (PLTP) activity were determined in plasma from 18 normolipidemic male patients with peripheral vascular disease and 21 controls. Furthermore, lecithin: cholesterol acyltransferase (LCAT) activity was tested. The results show that CETP mass, CETP activity, and LCAT activity are not different between patients and controls. However, specific CETP activity (CETP activity/CETP mass) is lower in the patients (P < .02). On the contrary, higher CET is observed in patients' plasma (P < .001). Increased plasma PLTP activity (P = .052) is demonstrable in the patients. If the data of all subjects are combined, CET correlates positively with triglycerides ([TG], r = .45, P < .001) and with PLTP activity (r = .32, P < .05) but negatively with specific CETP activity (r = -.37 P < .05). CET and specific CETP activity remain significantly different in TG-matched patients and controls and are more strongly interrelated (r = -.71, P < .001), suggesting a higher and selective influence of lipid transfer inhibitor(s) on CET and CETP activity in the patients. CET allows the best discrimination between patients and controls in univariate and multivariate analysis. Eighty-eight percent of the subjects are correctly classified by CET as a single parameter. The results suggest that increased CET in the patients may reflect atherogenic alterations in TG metabolism and/or in lipid transfer protein activities despite normal fasting lipoprotein levels.

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?

Long-chain n-3 polyunsaturated fatty acids and triacylglycerol metabolism in the postprandial state

Elevated plasma triacylglycerol (TG; triglyceride) concentrations, especially in the postprandial state, have been associated with an increased risk of coronary heart disease (CHD). Postprandial lipemia represents a complex series of reactions which occur following the ingestion of a meal containing fat and is associated with a number of adverse metabolic events including the production of atherogenic chylomicron remnants, the formation of the highly atherogenic small dense low density lipoprotein particles, a reduction in the concentration of the cardioprotective high density lipoprotein fraction and the activation of coagulation factor VII. Fish oils are a rich source of the long-chain n-3 polyunsaturated fatty acids (PUFA), eicosapentaenoic acid and docosahexaenoic acid. Long chain n-3 PUFA are effective hypotriglyceridemic agents, lowering both fasting and postprandial TG concentrations. There is a large body of evidence which shows that n-3 PUFA reduces plasma TG concentrations through reduced endogenous very low density lipoprotein production. This in turn may account for the reduced postprandial lipemic response following n-3 PUFA supplementation. However, this does not preclude a contribution of enhanced chylomicron clearance, which may be mediated through altered chylomicron size, structure or chemical composition, or altered lipoprotein lipase metabolism in terms of enzyme concentration, activity, or affinity for chylomicrons. However the precise biochemical nature of this effect remains to be established. The reduction of postprandial plasma TG concentrations by n-3 PUFA may partly explain why n-3 PUFA intake is inversely related to CHD mortality.

(n-3) fatty acid supplementation in moderately hypertriglyceridemic adults changes postprandial lipid and apolipoprotein B responses to a standardized test meal

The effects of (n-3) fatty acids on the postprandial state were investigated by monitoring the alimentary responses to identical test meals fed to adults [n = 11; fasting triacylglycerol (TG) 2.55 +/- 0.24 mmol/L; mean +/- SEM] after a self-selected diet baseline period (BLP) and then after a 6-wk (n-3) fatty acid period (FOP) [ approximately 5.2 g (n-3) fatty acids] and a 6-wk control oil period (COP) administered in random order. Samples were drawn immediately prior to the test meal (time 0) and then hourly from 2 to 6 h postmeal. Postprandial plasma triacylglycerol (TG) and TG-rich lipoprotein (TRL) TG apo B48, and B100 absolute concentrations were significantly lower after FOP than after COP or BLP, while plasma cholesterol was unchanged. Normalizing the results as increments over time 0 eliminated the diet effect on all but plasma TG. Time remained a significant effect for plasma TG, TRL TG, and TRL TC. Finally, only absolute TRL B48 and absolute and incremental plasma TG concentrations displayed significant time-diet interactions. These results suggest that postprandial TRL apo B reductions are likely caused by (n-3) fatty acid suppression of both hepatic and intestinal apoB secretion/synthesis. Altered TRL metabolism, i.e. changes in postprandial TG, cholesterol, apo B48, and increase in LDL particle size, may represent an additional mechanism for the reduced heart disease risk associated with fish [(n-3) fatty acid] consumption.

Understanding coronary heart disease as a consequence of defective regulation of apolipoprotein B metabolism

Further understanding of the causative link between plasma lipids and coronary heart disease will come from a deeper appreciation of the impact of lipoprotein heterogeneity on the processes of atherosclerosis and thrombosis. It is now widely appreciated that remnants of triglyceride-rich lipoproteins, IDL and specific LDL subfractions may have a role in atherogenesis disproportionate to the plasma concentrations of these species. Elucidation of the factors that control the distribution of subfractions within the spectrum of apolipoprotein B-containing lipoproteins is underway but far from complete. Important influences are the rate and nature of lipoproteins secreted from the liver, the extent of remodelling by lipid exchange and lipolysis in the circulation and the affinity of the various particles for cell surface receptors.

Influence of mild to moderately elevated triglycerides on low density lipoprotein subfraction concentration and composition in healthy men with low high density lipoprotein cholesterol levels

Epidemiologic studies have shown that a dyslipoproteinemia with low concentrations of high density lipoprotein (HDL) cholesterol and elevated serum triglycerides (TG) is associated with a particularly high incidence of coronary artery disease. This lipid profile is associated with increased concentrations of small, dense low density lipoprotein (LDL) particles. To evaluate the role of mild to moderately elevated TG on the LDL subfraction profile in patients with low HDL cholesterol, concentration and composition of six LDL subfractions was determined by density gradient ultracentrifugation in 41 healthy men (31+/-9 years, body mass index (BMI) 25.1+/-3.9 kg/m2) with equally low HDL cholesterol levels < 0.91 mmol/l but different TG levels: TG < 1.13 mmol/l, n = 16; TG = 1.13-2.26 mmol/l, n = 13: TG = 2.26-3.39 mmol/l, n = 12. Those men with moderately elevated TG levels between 2.26 and 3.39 mmol/l had significantly higher concentrations of very low density lipoprotein (VLDL), intermediate low density lipoprotein (IDL), and small, dense LDL apoB and cholesterol than men with TG < 1.13 mmol/l. With increasing serum TG, the TG content per particle also increased in VLDL, IDL as well as total LDL particles while the cholesterol and phospholipid (PL) content decreased in VLDL and IDL, but not in LDL particles. LDL subfraction analysis revealed that only large, more buoyant LDL particles (d < 1.044 g/ml) but not the smaller, more dense LDL, were enriched in TG. Small, dense LDL particles were depleted of free cholesterol (FC) and PL. This study has shown that in men with low HDL cholesterol levels mild to moderately elevated serum TG strongly suggest the presence of other metabolic cardiovascular risk factors and in particular of a more atherogenic LDL subfraction profile of increased concentration of small, dense LDL particles that are depleted in surface lipids.