Postprandial lipaemia and haemostatic factors

The Impact of Dietary Glycemic Index and Glycemic Load on Postprandial Lipid Kinetics, Dyslipidemia and Cardiovascular Risk

Many recent studies have acknowledged postprandial hypetriglyceridemia as a distinct risk factor for cardiovascular disease. This dysmetabolic state is the result of the hepatic overproduction of very low-density lipoproteins (VLDLs) and intestinal secretion of chylomicrons (CMs), which leads to highly atherogenic particles and endothelial inflammation. Postprandial lipid metabolism does not only depend on consumed fat but also on the other classes of nutrients that a meal contains. Various mechanisms through which carbohydrates exacerbate lipidemia have been identified, especially for fructose, which stimulates de novo lipogenesis. Glycemic index and glycemic load, despite their intrinsic limitations, have been used as markers of the postprandial glucose and insulin response, and their association with metabolic health and cardiovascular events has been extensively studied with contradictory results. This review aims to discuss the importance and pathogenesis of postprandial hypertriglyceridemia and its association with cardiovascular disease. Then, we describe the mechanisms through which carbohydrates influence lipidemia and, through a brief presentation of the available clinical studies on glycemic index/glycemic load, we discuss the association of these indices with atherogenic dyslipidemia and address possible concerns and implications for everyday practice.

Swim exercise inhibits hemostatic abnormalities in a rat model of obesity and insulin resistance

BACKGROUND

We sought to determine whether swim exercise can inhibit high carbohydrate and fat diet (HCFD)-induced biomarkers of coagulation and thrombosis.

MATERIAL AND METHODS

Rats were either fed with HCFD (model group) or a standard laboratory chow (control group) for 15 weeks. Swim exercise-'treated' rats started swim exercise training from the 11^th week until being sacrificed, on Week 15.

RESULTS

HCFD caused a significant increase in blood glucose, insulin resistance (HOMA-IR), lipidemia, and inflammatory biomarkers. In addition, HCFD significantly modulated coagulation and thrombosis biomarkers; fibrinogen, plasminogen activator inhibitor-1, von Willebrand factor, prothrombin time, activated partial thromboplastin time, blood clotting and bleeding time, and ADP-induced platelet aggregation that was effectively inhibited by swimming exercises.

CONCLUSIONS

We demonstrate that in an animal model of obesity and insulin resistance, there is a significant change in hemostasis, which is ameliorated by swim exercise.

How it all starts: Initiation of the clotting cascade

The plasma coagulation system in mammalian blood consists of a cascade of enzyme activation events in which serine proteases activate the proteins (proenzymes and procofactors) in the next step of the cascade via limited proteolysis. The ultimate outcome is the polymerization of fibrin and the activation of platelets, leading to a blood clot. This process is protective, as it prevents excessive blood loss following injury (normal hemostasis). Unfortunately, the blood clotting system can also lead to unwanted blood clots inside blood vessels (pathologic thrombosis), which is a leading cause of disability and death in the developed world. There are two main mechanisms for triggering the blood clotting, termed the tissue factor pathway and the contact pathway. Only one of these pathways (the tissue factor pathway) functions in normal hemostasis. Both pathways, however, are thought to contribute to thrombosis. An emerging concept is that the contact pathway functions in host pathogen defenses. This review focuses on how the initiation phase of the blood clotting cascade is regulated in both pathways, with a discussion of the contributions of these pathways to hemostasis versus thrombosis.

Triacylglycerol structure and interesterification of palmitic and stearic acid-rich fats: an overview and implications for cardiovascular disease

The position of fatty acids in the TAG molecule (sn-1, sn-2 and sn-3) determines the physical properties of the fat, which affects its absorption, metabolism and distribution into tissues, which may have implications for the risk of CHD. The TAG structure of fats can be manipulated by the process of interesterification, which is of increasing commercial importance, as it can be used to change the physical characteristics of a fat without the generation of trans-fatty acids. Interesterified fats rich in long-chain SFA are commercially important, but few studies have investigated their health effects. Evidence from animal and human infant studies suggests that TAG structure and interesterification affect digestibility, atherogenicity and fasting lipid levels, with fats containing palmitic and stearic acid in the sn-2 position being better digested and considered to be more atherogenic. However, chronic studies in human adults suggest that TAG structure has no effect on digestibility or fasting lipids. The postprandial effects of fats with differing TAG structure are better characterised but the evidence is inconclusive; it is probable that differences in the physical characteristics of fats resulting from interesterification and changes in TAG structure are key determinants of the level of postprandial lipaemia, rather than the position of fatty acids in the TAG. The present review gives an overview of TAG structure and interesterified palmitic and stearic acid-rich fats, their physical properties and their acute and chronic effects in human adults in relation to CHD.

Impaired postprandial endothelial function depends on the type of fat consumed by healthy men

Postprandial lipemia impairs endothelial function possibly via an oxidative stress mechanism. A stearic acid-rich triacylglycerol (TAG) (shea butter) results in a blunted postprandial increase in plasma TAG compared with an oleic acid-rich TAG; however, its acute effects on endothelial function and oxidative stress are unknown. A randomized crossover trial (n = 17 men) compared the effects of 50 g fat, rich in stearic acid [shea butter blend (SA)] or oleic acid [high oleic sunflower oil (HO)], on changes in endothelial function [brachial artery flow-mediated dilatation (FMD)], arterial tone [pulse wave analysis (PWA), and carotid-femoral pulse wave velocity (PWV(c-f))], and oxidative stress (plasma 8-isoprostane F2alpha) at fasting and 3 h following the test meals. The postprandial increase in plasma TAG was lower (66% lower incremental area under curve) following the SA meal [28.3 (9.7, 46.9)] than after the HO meal [83.4 (57.0, 109.8); P < 0.001] (geometric means with 95% CI, arbitary units). Following the HO meal, there was a decrease in FMD [-3.0% (-4.4, -1.6); P < 0.001] and an increase in plasma 8-isoprostane F2alpha [10.4ng/L (3.8, 16.9); P = 0.005] compared with fasting values, but no changes followed the SA meal. The changes in 8-isoprostane F2alpha and FMD differed between meals and were 14.0 ng/L (6.4, 21.6; P = 0.001) and 1.75% (0.10, 3.39; P = 0.02), respectively. The reductions in PWA and PWV c-f did not differ between meals. This study demonstrates that a stearic acid-rich fat attenuates the postprandial impairment in endothelial function compared with an oleic acid-rich fat and supports the hypothesis that postprandial lipemia impairs endothelial function via an increase in oxidative stress.

Manipulation of lipid bioaccessibility of almond seeds influences postprandial lipemia in healthy human subjects

BACKGROUND

Plant cell walls are known to influence the rate and extent of lipid release from plant food tissues during digestion; however, the effect of cell wall structure on postprandial lipemia is unknown.

OBJECTIVE

The objective was to investigate the effects of lipid release (bioaccessibility) on postprandial lipemia by comparing lipid encapsulated by cell walls with lipid present as free oil.

DESIGN

A randomized crossover trial (n = 20 men) compared the effects of 3 meals containing 54 g fat provided as whole almond seed macroparticles (WA), almond oil and defatted almond flour (AO), or a sunflower oil blend as control (CO) on postprandial changes in oxidative stress (8-isoprostane F(2)alpha concentrations), vascular tone (peripheral augmentation index), and plasma triacylglycerol, glucose, and insulin concentrations.

RESULTS

The postprandial increase in plasma triacylglycerol was lower [74% and 58% lower incremental area under curve (iAUC)] after the WA meal than after the AO and CO meals (P < 0.001). Increases in plasma glucose concentrations (0-180 min) were significantly higher after the WA meal (iAUC: 114; 95% CI: 76, 153) than after the AO meal (iAUC: 74; 95% CI: 48, 99) (P < 0.05), but no significant differences from the CO meal were observed (iAUC: 88; 95% CI: 66, 109). The peak reductions in peripheral augmentation index after the WA, AO, and CO meals (-9.5%, -10.1%, and -12.6%, respectively, at 2 h) were not significantly different between meals. Plasma 8-isoprostane F(2)alpha and insulin concentrations did not differ significantly between meals.

CONCLUSIONS

The bioaccessibility of lipid in almond seeds, which is regulated by the structure and properties of cell walls, plays a primary role in determining postprandial lipemia.

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.

Cholesterol absorption inhibitors: defining new options in lipid management

Although many studies have documented that reduction of plasma cholesterol levels decreases the risk of coronary artery disease, it remains the most common cause of death in the Western world. Current therapeutic options are effective in lowering cholesterol, especially in clinical trials, but clinical application is not optimized for many reasons. Dietary restriction for long-term management of hypercholesterolemia is helpful but usually insufficient to reduce low-density lipoprotein cholesterol (LDL-C) to goal levels. Powerful drugs are available, but these are often insufficient to meet the clinical demands for cholesterol-lowering therapy. Phytosterols and phytostanols have been partially effective by providing some inhibition of absorption of cholesterol. Compounds that specifically and more effectively block intestinal absorption of dietary and biliary cholesterol should provide a significant new agent for altering lipoprotein concentrations favorably. Ezetimibe is the first of this class of compounds that act at the gut epithelium to reduce cholesterol absorption in the milligram dose range markedly. Clinical studies indicate that ezetimibe effectively decreases LDL-C by 15 to 20% as monotherapy, with a favorable safety profile. Moreover, results from preliminary clinical trials indicate that ezetimibe given concomitantly with a statin provides additive efficacy. The combination represents a new approach to lipid management, achieving greater LDL-C and triglyceride reductions and greater improvements in HDL-C than statin monotherapy. This could offer another important option in clinical practice for management of hypercholesterolemic patients.

Postprandial Lipemia and Remnant Lipoproteins

Increased postprandial lipemia or elevated levels of triglyceride-rich remnant lipoproteins in fasting plasma are associated with increased risk of coronary artery disease. Despite many studies showing that postprandial triglyceride-rich lipoproteins play a central role in the pathogenesis of atherosclerosis, suitably standardized methods to measure postprandial lipemia or remnant lipoproteins in the clinical setting are lacking. This approach for cardiovascular risk assessment is confined to research laboratories and for the time being is not a standard procedure in clinical practice.

High postprandial triglyceridemia in patients with type 2 diabetes and microalbuminuria

Microalbuminuria (MA) is an independent risk factor for atherosclerosis in patients with type 2 diabetes mellitus (T2DM). Postprandial lipemia is also associated with excess cardiovascular risk. However, the association between MA and postprandial lipemia in diabetes has not been investigated. A total of 64 patients with T2DM, 30 with and 34 without MA, were examined. Plasma total triglycerides (TGs), triglycerides contained in chylomicrons (CM-TG), and TGs in CM-deficient plasma were measured at baseline and every 2 h for 6 h after a mixed meal. Postheparin LPL and HL activities were also determined. Plasma levels of apolipoprotein A-V (apoA-V), apoC-II, and apoC-III were measured in the fasting state and 2 h postprandially. Patients with MA had higher postprandial total TG levels than those without MA (P < 0.001); this increase been attributed mainly to CM-TG. LPL activity and fasting concentrations of the measured apolipoproteins were not different between the studied groups, whereas HL activity was higher in the patients with MA. ApoC-II and apoC-III levels did not change postprandially in either study group, whereas apoA-V increased more in the patients with MA. These data demonstrate for the first time that MA is characterized by increased postprandial lipemia in patients with T2DM and may explain in part the excess cardiovascular risk in these patients.

Plasma coagulation factor VII activity and its correlates in healthy men

OBJECTIVE

The aim of this study was to investigate the plasma coagulation factor VII activity and its correlates in healthy Australian men.

DESIGN

Cross-sectional study.

SETTING

Free living subjects.

SUBJECTS

A total of 139 healthy Australian males aged 20-55 y with widely varying intakes of individual fatty acids.

OUTCOME MEASURES

The concentration of phospholipid fatty acids and the parameters of biochemistry were analysed by standard methods. Citrated plasma factor VII activity was measured by using the ACL 200 system with commercially available kits.

RESULTS

In the stepwise multiple regression, controlled for age, body mass index and dietary groups, the two most important variables of factor VII activity were selected in the forward entry model with R (2) = 0.474 and P < 0.0001 from 19 independent variables, which were significantly correlated with plasma factor VII activity in age-adjusted bivariate analysis where significance was considered at P < 0.01. Plasma factor VII activity was strongly negatively correlated with prothrombin time (PT) (Std. Coeff. -0.550), and significantly positively correlated with plasma phospholipid (PL) stearic acid (Std. Coeff. 0.285).

CONCLUSIONS

Increased factor VII activity was associated with shortening of PT. All types of fatty-acid concentrations of PLs were significantly positively correlated with factor VII activity; however, stearic acid was more potent than other fatty acids in healthy Australian men.

SPONSORSHIP

Meat Research Corporation of Australia.

Effects on blood glucose, insulin, lipid and proatherosclerotic parameters in stable type 2 diabetic subjects during an oral fat challenge

BACKGROUND

Restriction of fat intake has been effective in improving insulin sensitivity in obese and type 2 diabetic subjects, but what effects the recommended diet (less than 30% of total calories from fat) have not been elucidated in subjects with type 2 diabetes. The purpose of this study was to test the effects of oral fat challenge, composing 30% calories of a meal, on blood glucose, insulin, lipid, leptin, plasminogen activator inhibitor-1 (PAI-1) and tumor necrosis factor-alpha (TNF-alpha).

DESIGN AND METHODS

Blood glucose, insulin, lipid, leptin, TNF-alpha and PAI-1 were compared in 14 type 2 diabetic patients and 10 normal subjects after an oral fat challenge upto 2 hours (fasting, 15 min, 30 min, 45 min, 60 min, 90 min and 120 min).

RESULTS

Postprandial glucose, total cholesterol, leptin, PAI-1 levels did not differ significantly from levels at fasting. Serum triglyceride increased significantly from baseline only in diabetic patients (P = 0.042). Serum insulin increased postprandially in both groups (P = 0.028 in diabetic group and P = 0.055 in normal group), with displaying a prolonged insulin response in diabetic subjects. TNF-alpha decreased postprandially in both groups without significant difference, although diabetic patients have higher baseline levels (P = 0.024 compared to normal subjects).

CONCLUSIONS

Oral fat load does not have an acute effect on blood glucose, total cholesterol, leptin and PAI-1 levels in both type 2 diabetic and normal subjects. TNF-alpha value showed decreased trend in both diabetic and normal subjects. The tendency of a delayed postprandial insulin response and elevated serum triglyceride level in diabetic subjects might be related to insulin resistance at the level of adipose tissue. Additional research is needed to assess the impact of the use of fat contents on the macronutrient composition of the diet, and potentially healthy and nutritional benefits for patients with diabetes.

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.

Postprandial lipemia is associated with platelet and monocyte activation and increased monocyte cytokine expression in normolipemic men

The activation of platelets and monocytes has been implicated in the development of cardiovascular diseases. We asked the question if postprandial lipemia following a fat- containing meal is associated with platelet and monocyte activation and increased platelet-monocyte interaction. Thirteen healthy, normal weight, normolipemic males, 20 to 49 years, consumed a 40% fat meal of whole foods. Blood samples were obtained at fasting and 3 1/2 and 6 hours after ingestion. Triglyceride levels increased to 48% over baseline at 3 1/2 hours postconsumption and returned to fasting levels by 6 hours. Multiparameter flow cytometry using monoclonal antibodies showed that the percentage of platelets expressing surface P-selectin and the activated conformation the GPIIb-IIa receptor was significantly higher at 3 1/2 hours compared to fasting. The percentage of platelet-monocyte aggregates increased by 36% at 3 1/2 hours and 43% at 6 hours postconsumption. The percentage of monocytes expressing intracellular tumor necrosis factor-alpha (TNF-alpha) increased seven and eightfold at 3 1/2 and 6 hours, respectively. The expression of interleukin-1beta (IL-1beta increased in a similar manner. These data suggest activation of platelets and monocytes after a moderate fat meal. Repetitive activation of platelets and monocytes could be an early event in the initiation and development of atherosclerosis.