Ethanol with a mixed meal increases postprandial triacylglycerol but decreases postprandial non-esterified fatty acid concentrations

Biosynthesis and Metabolism of ApoB-Containing Lipoproteins

Recent advances in human genetics, together with a substantial body of epidemiological, preclinical and clinical trial evidence, strongly support a causal relationship between triglyceride-rich lipoproteins (TRLs) and atherosclerotic cardiovascular disease. Consequently, the secretion and metabolism of TRLs have a significant impact on cardiovascular health. This knowledge underscores the importance of understanding the molecular mechanisms and regulation of very-low-density lipoprotein (VLDL) and chylomicron biogenesis. Fortunately, there has been a resurgence of interest in the intracellular assembly, trafficking, degradation, and secretion of VLDL, leading to many ground-breaking molecular insights. Furthermore, the identification of molecular control mechanisms related to triglyceride metabolism has greatly advanced our understanding of the complex metabolism of TRLs. In this review, we explore recent advances in the assembly, secretion, and metabolism of TRLs. We also discuss available treatment strategies for hypertriglyceridemia.

Research gaps and opportunities in precision nutrition: an NIH workshop report

Precision nutrition is an emerging concept that aims to develop nutrition recommendations tailored to different people's circumstances and biological characteristics. Responses to dietary change and the resulting health outcomes from consuming different diets may vary significantly between people based on interactions between their genetic backgrounds, physiology, microbiome, underlying health status, behaviors, social influences, and environmental exposures. On 11-12 January 2021, the National Institutes of Health convened a workshop entitled "Precision Nutrition: Research Gaps and Opportunities" to bring together experts to discuss the issues involved in better understanding and addressing precision nutrition. The workshop proceeded in 3 parts: part I covered many aspects of genetics and physiology that mediate the links between nutrient intake and health conditions such as cardiovascular disease, Alzheimer disease, and cancer; part II reviewed potential contributors to interindividual variability in dietary exposures and responses such as baseline nutritional status, circadian rhythm/sleep, environmental exposures, sensory properties of food, stress, inflammation, and the social determinants of health; part III presented the need for systems approaches, with new methods and technologies that can facilitate the study and implementation of precision nutrition, and workforce development needed to create a new generation of researchers. The workshop concluded that much research will be needed before more precise nutrition recommendations can be achieved. This includes better understanding and accounting for variables such as age, sex, ethnicity, medical history, genetics, and social and environmental factors. The advent of new methods and technologies and the availability of considerably more data bring tremendous opportunity. However, the field must proceed with appropriate levels of caution and make sure the factors listed above are all considered, and systems approaches and methods are incorporated. It will be important to develop and train an expanded workforce with the goal of reducing health disparities and improving precision nutritional advice for all Americans.

Metabolism of triglyceride-rich lipoproteins in health and dyslipidaemia

Accumulating evidence points to the causal role of triglyceride-rich lipoproteins and their cholesterol-enriched remnants in atherogenesis. Genetic studies in particular have not only revealed a relationship between plasma triglyceride levels and the risk of atherosclerotic cardiovascular disease, but have also identified key proteins responsible for the regulation of triglyceride transport. Kinetic studies in humans using stable isotope tracers have been especially useful in delineating the function of these proteins and revealing the hitherto unappreciated complexity of triglyceride-rich lipoprotein metabolism. Given that triglyceride is an essential energy source for mammals, triglyceride transport is regulated by numerous mechanisms that balance availability with the energy demands of the body. Ongoing investigations are focused on determining the consequences of dysregulation as a result of either dietary imprudence or genetic variation that increases the risk of atherosclerosis and pancreatitis. The identification of molecular control mechanisms involved in triglyceride metabolism has laid the groundwork for a 'precision-medicine' approach to therapy. Novel pharmacological agents under development have specific molecular targets within a regulatory framework, and their deployment heralds a new era in lipid-lowering-mediated prevention of disease. In this Review, we outline what is known about the dysregulation of triglyceride transport in human hypertriglyceridaemia.

Metabolism of Triglyceride-Rich Lipoproteins

Triglycerides are critical lipids as they provide an energy source that is both compact and efficient. Due to its hydrophobic nature triglyceride molecules can pack together densely and so be stored in adipose tissue. To be transported in the aqueous medium of plasma, triglycerides have to be incorporated into lipoprotein particles along with other components such as cholesterol, phospholipid and associated structural and regulatory apolipoproteins. Here we discuss the physiology of normal triglyceride metabolism, and how impaired metabolism induces hypertriglyceridemia and its pathogenic consequences including atherosclerosis. We also discuss established and novel therapies to reduce triglyceride-rich lipoproteins.

The Tailgate Study: Differing metabolic effects of a bout of excessive eating and drinking

INTRODUCTION

Excess energy intake by spectators at a sporting event (i.e., a tailgate) might cause acute negative health effects. However, limited data exist regarding the effects of overeating and alcohol consumption on lipid metabolism and the potential to gain intrahepatic triacylglycerols (IHTG). We tested the hypothesis that overconsumption of food and alcohol would significantly increase both hepatic de novo lipogenesis (DNL) and IHTG.

METHODS

Eighteen males (mean ± SD, age: 31.4 ± 7.3 years, BMI: 32.1 ± 5.9 kg/m²) were given alcoholic drinks to elevate blood alcohol for 5 h, while highly palatable food was presented. Blood samples were collected and DNL in TG-rich lipoproteins (TRL) was measured by GC/MS, IHTG was measured via MRS (n = 15), and substrate oxidation was measured via indirect calorimetry.

RESULTS

Subjects consumed 5087 ± 149 kcal (191 ± 25% excess of total daily energy needs including 171 ± 24 g alcohol), which increased plasma insulin, glucose, TG, and decreased NEFA (ANOVA p ≤ 0.003 for all). Both DNL and TRL-TG increased (p < 0.001), while IHTG did not change in the group as a whole (p = 0.229). Individual subject data revealed remarkably differing responses for IHTG (nine increased, five decreased, one did not change). Despite maintaining equal breath alcohol levels, subjects with IHTG elevations exhibited higher DNL, consumed 90% less alcohol (p = 0.048), tended to consume more carbohydrates, and exhibited lower whole-body fat oxidation (not significant) compared to those whose IHTG was reduced.

DISCUSSION

This study demonstrates that acute excess energy intake may have differing effects on an individual's DNL and IHTG, and dietary carbohydrate may influence DNL more than alcohol.

The Influence of Different Foods and Food Ingredients on Acute Postprandial Triglyceride Response: A Systematic Literature Review and Meta-Analysis of Randomized Controlled Trials

The use of postprandial triglyceride (ppTG) as a cardiovascular disease risk indicator has gained recent popularity. However, the influence of different foods or food ingredients on the ppTG response has not been comprehensively characterized. A systematic literature review and meta-analysis was conducted to assess the effects of foods or food ingredients on the ppTG response. PubMed, MEDLINE, Cochrane, and CINAHL databases were searched for relevant acute (<24-h) randomized controlled trials published up to September 2018. Based on our selection criteria, 179 relevant trials (366 comparisons) were identified and systematically compiled into distinct food or food ingredient categories. A ppTG-lowering effect was noted for soluble fiber (Hedges' giAUC = -0.72; 95% CI: -1.33, -0.11), sodium bicarbonate mineral water (Hedges' gAUC = -0.42; 95% CI: -0.79, -0.04), diacylglycerol oil (Hedges' giAUC = -0.38; 95% CI: -0.75, -0.00), and whey protein when it was contrasted with other proteins. The fats group showed significant but opposite effects depending on the outcome measure used (Hedges' giAUC = -0.32; 95% CI: -0.61, -0.03; and Hedges' gAUC = 0.16; 95% CI: 0.06, 0.26). Data for other important food groups (nuts, vegetables, and polyphenols) were also assessed but of limited availability. Assessing for oral fat tolerance test (OFTT) recommendation compliance, most trials were ≥4 h long but lacked a sufficiently high fat challenge. iAUC and AUC were more common measures of ppTG. Overall, our analyses indicate that the effects on ppTG by different food groups are diverse, largely influenced by the type of food or food ingredient within the same group. The type of ppTG measurement can also influence the response.

Oral Glucose Mobilizes Triglyceride Stores From the Human Intestine

BACKGROUND & AIMS

The small intestine regulates plasma triglyceride (TG) concentration. Within enterocytes, dietary TGs are packaged into chylomicrons (CMs) for secretion or stored temporarily in cytoplasmic lipid droplets (CLDs) until further mobilization. We and others have shown that oral and intravenous glucose enhances CM particle secretion in human beings, however, the mechanisms through which this occurs are incompletely understood.

METHODS

Two separate cohorts of participants ingested a high-fat liquid meal and, 5 hours later, were assigned randomly to ingest either a glucose solution or an equivalent volume of water. In 1 group (N = 6), plasma and lipoprotein TG responses were assessed in a randomized cross-over study. In a separate group (N = 24), duodenal biopsy specimens were obtained 1 hour after ingestion of glucose or water. Ultrastructural and proteomic analyses were performed on duodenal biopsy specimens.

RESULTS

Compared with water, glucose ingestion increased circulating TGs within 30 minutes, mainly in the CM fraction. It decreased the total number of CLDs and the proportion of large-sized CLDs within enterocytes. We identified 2919 proteins in human duodenal tissue, 270 of which are related to lipid metabolism and 134 of which were differentially present in response to glucose compared with water ingestion.

CONCLUSIONS

Oral glucose mobilizes TGs stored within enterocyte CLDs to provide substrate for CM synthesis and secretion. Future studies elucidating the underlying signaling pathways may provide mechanistic insights that lead to the development of novel therapeutics for the treatment of hypertriglyceridemia.

Acute alcohol consumption downregulates lipoprotein lipase activity in vivo

OBJECTIVE

Acute alcohol consumption can induce hypertriglyceridemia. Such an effect could be explained in part by the influence of alcohol on lipoprotein lipase (LPL) - the key enzyme responsible for triglyceride hydrolysis in circulation. Therefore, we have studied the effects of acute moderate alcohol consumption on LPL activity and on the concentrations of angiopoietin-like proteins 3 and 4 (ANGPTL3 and ANGPTL4), which are known to inhibit LPL.

METHODS

Two experiments were carried out in 8 healthy volunteers. They received 25 g of alcohol (vodka) in one experiment and water in the other (control). The in vivo function of LPL was estimated using intravenous fat tolerance tests (IVFTT) carried out before, 2 and 4 hours after alcohol administration. At the end of each experiment, LPL activity and mass were measured in post-heparin plasma (PHP). The concentrations of ANGPTL3 and ANGPTL4 in blood were measured before alcohol consumption and at the end of the experiments.

RESULTS

LPL activity, as estimated using the IVFTT, was reduced by 25% and 24% two and four hours after the administration of alcohol, respectively, and was not affected in the control experiment. At the end of the experiment, LPL activity in PHP was 23% lower after alcohol consumption than in the controls. The concentrations of ANGPTL3 and ANGPTL4 had dropped to 67% and 86% of baseline values, respectively, at 280 min after alcohol consumption. These levels were not affected in the control experiment. The levels of ANGPTL4 but not those of ANGPTL3 were increased in PHP compared to both baseline values and values at 280 min.

CONCLUSION

The capacity for triglyceride clearance seemed to be acutely reduced by alcohol consumption and the effect persisted for several hours. The levels of LPL activity in PHP were reduced to a similar extent. This reduction in LPL activity could not be explained by the changes in the levels of ANGPTL3 or ANGPTL4, which both decreased.

Postprandial lipemia as a cardiometabolic risk factor

High levels of fasting circulating triglycerides (TG) represent an independent risk factor for cardiovascular disease. In western countries, however, people spend most time in postprandial conditions, with continuous fluctuation of lipemia due to increased levels of TG-rich lipoproteins (TRLs), including chylomicrons (CM), very low density lipoproteins (VLDL), and their remnants. Several factors contribute to postprandial lipid metabolism, including dietary, physiological, pathological and genetic factors. The presence of coronary heart disease, type 2 diabetes, insulin resistance and obesity is associated with higher postprandial TG levels compared with healthy conditions; this association is present also in subjects with normal fasting TG levels. Increasing evidence indicates that impaired metabolism of postprandial lipoproteins contributes to the pathogenesis of coronary artery disease, suggesting that lifestyle modifications as well as pharmacological approaches aimed at reducing postprandial TG levels might help to decrease the cardiovascular risk.

Nuclear factor (erythroid-derived 2)-like 2 activation-induced hepatic very-low-density lipoprotein receptor overexpression in response to oxidative stress contributes to alcoholic liver disease in mice

Chronic alcohol consumption leads to hypertriglyceridemia, which is positively associated with alcoholic liver disease (ALD). However, whether and how it contributes to the development of fatty liver and liver injury are largely unknown. In this study we demonstrate that chronic alcohol exposure differently regulates the expression of very-low-density lipoprotein receptor (VLDLR) in adipose tissue and the liver. Whereas adipose tissue VLDLR is significantly down-regulated, its hepatic expression is dramatically increased after chronic alcohol feeding. While HepG2 cells stably overexpressing VLDLR manifests increased intracellular triglyceride accumulation, VLDLR-deficient mice are protective against fatty liver and liver injury after chronic alcohol exposure. Mechanistic investigations using both in vitro and in vivo systems reveal that oxidative stress-induced nuclear factor (erythroid-derived 2)-like 2 (Nrf2) activation plays a critical role in alcohol-induced VLDLR up-regulation in hepatocytes, but not in adipocytes. Oxidative stress enhances VLDLR gene expression and protein abundance in primary hepatocytes, concomitant with the Nrf2 activation. Conversely, Nrf2 gene silencing abrogates oxidative stress-induced VLDLR up-regulation in the liver, but not in adipose tissue. In mice, alcohol exposure induces hepatic oxidative stress and Nrf2 activation. Supplementation of N-acetylcysteine alleviates fatty liver and liver injury induced by chronic alcohol exposure, which is associated with suppressed Nrf2 activation and attenuated VLDLR increase in the liver. Furthermore, in comparison to wild-type counterparts, Nrf2-deficient mice demonstrate attenuated hepatic VLDLR expression increase in response to chronic alcohol exposure.

CONCLUSION

Chronic alcohol consumption differently alters VLDLR expression in adipose tissue and the liver. Oxidative stress-induced Nrf2 activation is mechanistically involved in VLDLR overexpression in hepatocytes in response to chronic alcohol consumption. Hepatic VLDLR overexpression plays an important role in the pathogenesis of ALD.

Anti-fatty liver effects of oils from Zingiber officinale and Curcuma longa on ethanol-induced fatty liver in rats

OBJECTIVE

The present study is aimed at evaluating the protective effects of oils from Zingiber officinale (ginger) and Curcuma longa (turmeric) on acute ethanol-induced fatty liver in male Wistar rats.

METHODS

Ferric reducing antioxidant power activity and oxygen radical absorbance capacity of the oils were evaluated ex vivo. Rats were pretreated for 28 d with standard drug (Livolin Forte) and oils from Z. officinale and C. longa before they were exposed to 45% ethanol (4.8 g/kg) to induce acute fatty liver. Histological changes were observed and the degree of protection was measured by using biochemical parameters such as alanine aminotransferase, aspartate aminotransferase and alkaline phosphatase activities. Serum triglyceride (TG) level, total cholesterol (TC) level and the effects of both oils on reduced gluthatione (GSH), glutathione-S-transferase (GST), superoxide dismutase (SOD) and hepatic malondialdehyde (MDA) levels were estimated.

RESULTS

Oils from Z. officinale and C. longa at a dose of 200 mg/kg showed hepatoprotection by decreasing the activities of serum enzymes, serum TG, serum TC and hepatic MDA, while they significantly restored the level of GSH as well as GST and SOD activities. Histological examination of rats tissues was related to the obtained results.

CONCLUSION

From the results it may be concluded that oils from Z. officinale and C. longa (200 mg/kg) exhibited hepatoprotective activity in acute ethanol-induced fatty liver and Z. officinale oil was identified to have better effects than C. longa oil.

Postprandial triglyceridemia after single dose of alcohol in healthy young men

BACKGROUND AND AIMS

Moderate alcohol consumption provides protection against cardiovascular disease primarily due to increase of HDL-cholesterol. However, it also has some adverse effects on metabolism of triglycerides (TG). Therefore, we addressed the question how a single dose of alcohol affects postprandial lipemia and activities of two enzymes playing a critical role in regulation of triglyceridemia, lipoprotein lipase (LPL) and hepatic triglyceride lipase (HTGL).

METHODS AND RESULTS

Eight healthy volunteers were given a single dose of alcohol (vodka; 0.6 g of ethanol/kg of body weight) together with a fat load (0.7 g of fat/kg of body weight) in an experimental breakfast or together with dinner 12 h before the experimental breakfast. In comparison to control experiment, alcohol given with breakfast induced increased and prolonged postprandial response of triglyceride-rich lipoproteins (TRL; d < 1.006 g/ml). At the same time TG accumulated also in intermediate density lipoproteins (IDL; d 1.006-1.019 g/ml). Alcohol given in the evening before the experiment increased fasting TG concentration but did not affect changes in TRL and IDL concentrations. LPL activity measured both in vivo using intravenous fat tolerance test and in vitro and HTGL activity were determined at the end of experiments (after 7.5 h of postprandial lipemia study). Neither was affected by a single dose of alcohol.

CONCLUSIONS

Single dose of alcohol induces immediate and profound changes in metabolism of TRL and IDL. The same dose of alcohol given 12 h before meal does affect baseline TG concentration but not the postprandial changes of triglyceridemia.

Modifying effects of alcohol on the postprandial glucose and insulin responses in healthy subjects

BACKGROUND

Moderate alcohol consumption associates with lower risk of type 2 diabetes, but in postprandial studies, alcohol induced impaired insulin sensitivity. The measurement of the glycemic index (GI) for beer has been considered challenging because of its low carbohydrate content. Therefore, imputed GI values from 36 to 95 on the basis of carbohydrate-rich beverages have been used for beer in epidemiologic studies.

OBJECTIVES

We investigated the acute effects of alcohol on glucose and insulin responses and measured GIs and insulinemic indexes (IIs) of nonalcoholic and alcoholic beers.

DESIGN

In a crossover design, 10 healthy volunteers were served beer with 4.5% alcohol by volume, nonalcoholic beer, and a glucose solution with alcohol once and the reference glucose solution twice. Each portion contained 25 g available carbohydrate, and the beer and glucose solution with alcohol contained 21 g alcohol. Capillary blood samples were collected up to 2 h after ingestion, and the incremental AUCs (IAUCs), GIs, and IIs were calculated.

RESULTS

Compared with the reference glucose solution, the glucose solution with alcohol produced an 18% higher postprandial glucose IAUC (P = 0.03) and had no significant effect on the insulin IAUC. Compared with the reference glucose solution, beer had no significant effect on glucose or insulin IAUCs, and nonalcoholic beer tended to reduce the glucose IAUC (P = 0.06) but not the insulin IAUC. GIs of beer and nonalcoholic beer were 119 and 80, and IIs were 130 and 88, respectively.

CONCLUSIONS

Alcohol increases the postprandial glucose response, probably through impaired insulin sensitivity. GI values published for alcohol-containing beers have underestimated the true glycemic effects.

Joint association of glycemic load and alcohol intake with type 2 diabetes incidence in women

BACKGROUND

Little is known about the joint association between glycemic index (GI), glycemic load (GL), and alcohol intake with type 2 diabetes (T2D).

OBJECTIVE

The objective of this study was to examine whether alcohol intake alters the associations between carbohydrate quality (GI) or quality and quantity (GL) and T2D incidence in women.

DESIGN

Participants from the Nurses' Health Study who were free of T2D, cardiovascular disease, or cancer (n = 81,827) at baseline in 1980 were followed for 26 y. Cumulative averages of GI, GL, total carbohydrates, and alcohol intake were calculated every 2-4 y from validated food-frequency questionnaires. Cox proportional hazard models were used to adjust for covariates.

RESULTS

We documented 6950 cases of T2D during follow-up. After adjustment for lifestyle and dietary factors, the positive association between GL and T2D risk was attenuated in subjects with higher alcohol intakes. RRs that compared the top and bottom quintiles of GL were 1.29 (95% CI: 1.11, 1.49; P-trend < 0.001) in women with alcohol intakes of 0 to <5 g/d, 1.34 (95% CI: 0.93, 1.92; P-trend = 0.05) in women with alcohol intakes of 5 to <15 g/d, and 0.99 (95% CI: 0.60, 1.65; P-trend = 0.82) in women with alcohol intakes ≥15 g/d (P-interaction = 0.02). However, a higher intake of alcohol did not modify the positive association between GI and T2D (P-interaction = 0.76).

CONCLUSION

Our findings suggest that a higher alcohol intake (≥15 g/d) attenuates the positive association between GL and T2D incidence.

The effect of alcohol on postprandial and fasting triglycerides

Alcohol has a significant additive effect on the postprandial triglyceride peak when it accompanies a meal containing fat, especially saturated fat. This results from a decrease in the breakdown of chylomicrons and VLDL remnants due to an acute inhibitory effect of alcohol on lipoprotein lipase activity. Furthermore, alcohol increases the synthesis of large VLDL particles in the liver, which is the main source of triglycerides in the hypertriglyceridemia associated with chronic excessive alcohol intake. In case of chronic consumption, lipoprotein lipase activity seems to adapt itself. The effect of alcohol on adipose tissues is less clear. Sometimes, a severe hypertriglyceridemia induced by alcohol (SHIBA) can be observed, especially in patients with type 2 diabetes mellitus and/or obesity increasing the risk of pancreatitis.

Positive relationship between dietary fat, ethanol intake, triglycerides, and hypothalamic peptides: counteraction by lipid-lowering drugs

Studies in both humans and animals suggest a positive relationship between the intake of ethanol and intake of fat, which may contribute to alcohol abuse. This relationship may be mediated, in part, by hypothalamic orexigenic peptides such as orexin (OX), which stimulate both consumption of ethanol and fat, and circulating triglycerides (TGs), which stimulate these peptides and promote consummatory behavior. The present study investigated this vicious cycle between ethanol and fat, to further characterize its relation to TGs and to test the effects of lowering TG levels. In Experiment 1, the behavioral relationship between fat intake and ethanol was confirmed. Adult male Sprague-Dawley rats, chronically injected intraperitoneally with ethanol (1g/kg) and tested in terms of their preference for a high-fat diet (HFD) compared with low-fat diet (LFD), showed a significant increase in their fat preference, compared with rats injected with saline, in measures of 2h and 24h intake. Experiment 2 tested the relationship of circulating TGs in this positive association between ethanol and fat, in rats chronically consuming 9% ethanol versus water and given acute meal tests (25kcal) of a HFD versus LFD. Levels of TGs were elevated in response to both chronic drinking of ethanol versus water and acute eating of a high-fat versus low-fat meal. Most importantly, ethanol and a HFD showed an interaction effect, whereby their combination produced a considerably larger increase in TG levels (+172%) compared to ethanol with a LFD (+111%). In Experiment 3, a direct manipulation of TG levels was found to affect ethanol intake. After intragastric administration of gemfibrozil (50mg/kg) compared with vehicle, TG levels were lowered by 37%, and ethanol intake was significantly reduced. In Experiment 4, the TG-lowering drug gemfibrozil also caused a significant reduction in the expression of the orexigenic peptide, OX, in the perifornical lateral hypothalamus. These results support the existence of a vicious cycle between ethanol and fat, whereby each nutrient stimulates intake of the other. Within this vicious cycle, ethanol and fat act synergistically to increase TG levels, which in turn stimulate peptides that promote further consumption, and these phenomena are reversed by gemfibrozil, which lowers TG levels.

Overproduction of very low-density lipoproteins is the hallmark of the dyslipidemia in the metabolic syndrome

Insulin resistance is a key feature of the metabolic syndrome and often progresses to type 2 diabetes. Both insulin resistance and type 2 diabetes are characterized by dyslipidemia, which is an important and common risk factor for cardiovascular disease. Diabetic dyslipidemia is a cluster of potentially atherogenic lipid and lipoprotein abnormalities that are metabolically interrelated. Recent evidence suggests that a fundamental defect is an overproduction of large very low-density lipoprotein (VLDL) particles, which initiates a sequence of lipoprotein changes, resulting in higher levels of remnant particles, smaller LDL, and lower levels of high-density liporotein (HDL) cholesterol. These atherogenic lipid abnormalities precede the diagnosis of type 2 diabetes by several years, and it is thus important to elucidate the mechanisms involved in the overproduction of large VLDL particles. Here, we review the pathophysiology of VLDL biosynthesis and metabolism in the metabolic syndrome. We also review recent research investigating the relation between hepatic accumulation of lipids and insulin resistance, and sources of fatty acids for liver fat and VLDL biosynthesis. Finally, we briefly discuss current treatments for lipid management of dyslipidemia and potential future therapeutic targets.

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.

Methodology for studying postprandial lipid metabolism

BACKGROUND

Postprandial lipid metabolism in humans has deserved much attention during the last two decades. Although fasting lipid and lipoprotein parameters reflect body homeostasis to some extent, the transient lipid and lipoprotein accumulation that occurs in the circulation after a fat-containing meal highlights the individual capacity to handle an acute fat input. An exacerbated postprandial accumulation of triglyceride-rich lipoproteins in the circulation has been associated with an increased cardiovascular risk.

METHODS

The important number of studies published in this field raises the question of the methodology used for such postprandial studies, as reviewed.

RESULTS

Based on our experiences, the present review reports and discuss the numerous methodological issues involved to serve as a basis for further works. These aspects include aims of the postprandial tests, size and nutrient composition of the test meals and background diets, pre-test conditions, characteristics of subjects involved, timing of sampling, suitable markers of postprandial lipid metabolism and calculations.

CONCLUSION

In conclusion, we stress the need for standardization of postprandial tests.

Effects of one single bout of low-intensity exercise on postprandial lipaemia in type 2 diabetic men

Fighting type 2 diabetes and its high risk of CVD, lifestyle intervention with diet and exercise is of uttermost importance. Epidemiological studies strongly suggest an inverse association between increased physical activity, moderate alcohol drinking and the incidence of both type 2 diabetes and CVD. However, alcohol is known to increase postprandial lipaemia, a risk marker of CVD, and exercise to reduce postprandial lipaemia in healthy individuals. The aim of the present study was to investigate how type 2 diabetic men respond, in the postprandial period, to a single exercise session feasible to perform on a daily basis for type 2 diabetic men. The twelve participants ingested a test meal containing 100 g butter, 50 g carbohydrate, together with 40 g alcohol, at each meal test, imitating a social meal situation. Two protocols included exercise sessions with 40 min at 40 % VO2max, one where they exercised 3·5 h after, and another the afternoon before the test meal. One protocol was without any exercise. No significant effect of low-intensity exercise on postprandial lipaemia following a fat-rich meal with alcohol was seen in the middle-aged type 2 diabetic men.

Effect of aerobic exercise on lipaemia and its fatty acid profile after a meal of moderate fat content in eumenorrhoeic women

Exercise prior to eating has repeatedly been shown to reduce postprandial lipaemia. The aim of the present study was to investigate whether this effect was manifest in the presence of two factors that independently mitigate postprandial lipaemia: eumenorrhoea and moderate fat intake. Eight healthy eumenorrhoeic rowers consumed a meal of moderate fat content (35 % total energy, 0.66 g/kg body mass) 14 h after having either rowed at 55 % of maximal aerobic power (81 % of maximal heart rate) for 80 min or rested. Both trials were performed during the luteal phase. Blood samples were drawn before the meal and for 8 h postprandially for the measurement of individual fatty acids in the triacylglycerol and NEFA fractions, as well as of glucose, insulin and oestradiol. Plasma oestradiol concentrations were not significantly different in the two trials. The postprandial lipaemic response, expressed as either plasma triacylglycerol concentration or area under the triacylglycerol-time curve, was 35 % lower (P<0.05) after exercise. The postprandial glycaemic and insulinaemic responses were also lower, indicating increased insulin sensitivity, whereas the NEFA response was higher, suggesting a lower entrapment of dietary fatty acids in adipose tissue after exercise. Finally, exercise increased the proportion of unsaturated:saturated NEFA during the postprandial period. In conclusion, aerobic exercise performed 14 h before a moderate-fat meal reduced postprandial lipaemia in women in the luteal phase. This effect shows the potential of exercise to mitigate even moderate lipaemic responses in eumenorrhoeic women.

Effects of ethanol on lipids and atherosclerosis

Moderate alcohol consumption is associated with an increase in plasma high density lipoprotein (HDL) cholesterol concentration and a decrease in low density lipoprotein (LDL) cholesterol concentration. Changes in the concentration and composition of lipoproteins are estimated to account for more than half of alcohol's protective effect for coronary heart disease. Alcohol intake also affects plasma proteins involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, and phospholipases. In addition, alcohol intake may result in acetaldehyde modification of apolipoproteins. Furthermore, "abnormal" lipids, phosphatidylethanol and fatty acid ethyl esters are formed in the presence of ethanol and are associated with lipoproteins in plasma. Ethanol and ethanol-induced modifications of lipids may modulate the effects of lipoproteins on the cells in the arterial wall. The molecular mechanisms involved in these processes are complex, requiring further study to better understand the specific effects of ethanol in the pathogenesis of atherosclerosis. This review discusses the effects of ethanol on lipoproteins and lipoprotein metabolism, as well as the novel effects of lipoproteins on vascular wall cells.

Comparative Effects of Curcumin and Its Analog on Alcohol- and Polyunsaturated Fatty Acid-Induced Alterations in Circulatory Lipid Profiles

Excessive alcohol intake induces hyperlipidemia. Studies suggest that natural principles and their analogs are known to possess anti-hyperlipidemic properties. In the present work we tested the effect of curcumin, an active principle of turmeric (Curcuma longa), and a curcumin analog on alcohol- and thermally oxidized polyunsaturated fatty acid (deltaPUFA)- induced hyperlipidemia. Male albino Wistar rats were used for the experimental study. Anti-hyperlipidemic activity of curcumin and curcumin analog was evaluated by analyzing the levels of cholesterol, triglycerides (TGs), phospholipids (PLs), and free fatty acids (FFAs). The results showed that the levels of cholesterol, TGs, PLs, and FFAs were increased significantly in alcohol-, deltaPUFA-, and alcohol + deltaPUFA-treated groups, which were brought down significantly on treatment with either of the curcuminoids. Curcumin analog treatment was found to be more effective than curcumin treatment. From the results obtained, we conclude that both curcumin and its analog effectively protect the system against alcohol- and deltaPUFA-induced hyperlipidemia and are possible candidates for the treatment of hyperlipidemia.

Beneficial postprandial effect of a small amount of alcohol on diabetes and cardiovascular risk factors: modification by insulin resistance

Moderate alcohol consumption protects against type 2 diabetes and cardiovascular disease. Because humans spend most of their time in the postprandial state, we examined the effect of 15 g alcohol on postprandial metabolic factors in 20 postmenopausal women over 6 h. We measured 1) glucose, insulin, lipids, C-reactive protein, and adiponectin levels; 2) augmentation index by applanation tonometry; and 3) energy expenditure and substrate oxidation by indirect calorimetry. Subjects received low carbohydrate (LC; visits 1 and 2) and high carbohydrate (HC; visits 3 and 4) high fat meals with and without alcohol. Alcohol augmented the postprandial increment in insulin (P = 0.07) and reduced the postprandial increment in glucose (P = 0.04) after the LC meal only. Triglycerides were increased by alcohol after the LC (P = 0.002) and HC (P = 0.008) meals. Total and high-density lipoprotein cholesterol, fatty acids, and total adiponectin responses were unaffected. C-reactive protein levels decreased postprandially; reductions were enhanced by alcohol after the HC meal, but were attenuated after the LC meal. Postprandial reductions in the augmentation index were increased by alcohol after the LC meal only (P = 0.007). Alcohol enhanced the postprandial increase in energy expenditure 30-60 min after the LC meal (increase, 373 +/- 49 vs. 236 +/- 32 kcal/d; P = 0.02) and HC meal (increase, 362 +/- 36 vs. 205 +/- 34 kcal/d; P = 0.0009), but suppressed fat and carbohydrate oxidation. Some of our findings may be mechanisms for lower diabetes and cardiovascular risks in moderate drinkers.

The effect of acute red wine polyphenol consumption on postprandial lipaemia in postmenopausal women

Postprandial lipoproteins are potentially atherogenic. The aim of this study was to elucidate whether acute consumption of red wine (RW) and dealcoholised red wine (DRW) regulates postprandial lipid and lipoprotein metabolism in 17 dyslipidaemic postmenopausal women. A mixed meal accompanied by either water, RW or DRW was consumed on three separate visits, in random order, 2 weeks apart. One fasting and 6 hourly postprandial blood samples were taken for lipid analysis. Results showed no significant quantitative changes in postprandial apolipoprotein (apo) B48 levels following the consumption of DRW or RW compared to water. However, qualitatively, DRW may reduce arterial exposure to apoB48-containing lipoproteins over the 6-h postprandial period measured. DRW consumption did not significantly change postprandial TG or insulin levels. A 35% (p = 0.02) increase in postprandial triglyceride (TG) levels and a 54% (p = 0.02) increase in insulin levels were observed following RW consumption, compared to water. In conclusion, acute DRW consumption had no effect on postprandial lipid and lipoprotein metabolism in dyslipidaemic postmenopausal women. However, the consumption of full-compliment RW exacerbated the postprandial lipaemic and insulin response over the 6-h period. Collectively, our findings suggest that neither polyphenols nor red wine reduce atherosclerotic risk by acutely modulating postprandial lipaemia over a 6-h period.

Effect of prior exercise on lipemia after a meal of moderate fat content

OBJECTIVE

Prior exercise has been repeatedly shown to reduce lipemia after meals of exaggerated fat content (over 60% of total energy). The aim of the present study was to investigate whether the same applies to meals closer to the composition of the typical Western diet and explore whether exercise affects the release of dietary fat into the bloodstream.

DESIGN

Randomized counterbalanced.

SETTING

Laboratory.

SUBJECTS

Nine healthy young male volunteers.

INTERVENTION

Subjects consumed a meal of moderate fat content (35% of total energy, 0.66 g/kg body mass) 14 h after having either cycled for 1 h at 70-75% of maximal heart rate or rested. Macadamia nuts were used as the main source of dietary fat to trace its entry into the circulation because of their unusual fatty acid composition. Blood samples were drawn before the meal and for 8 h postprandially.

RESULTS

Plasma triacylglycerol concentrations and total area under the triacylglycerol concentration vs time curve (AUC) were significantly lower after exercise (P = 0.001 and 0.003, respectively; effect size for the latter, 0.84). However, incremental (above baseline) AUC was not affected by exercise significantly. When controlling for differences in baseline plasma concentrations, only the fatty acids that were more abundant in the meal than in plasma triacylglycerols were decreased in the early postprandial period following exercise, implying either a suppressive effect of exercise on the rate of triacylglycerol release from the intestine or a more rapid chylomicron clearance after meal consumption.

CONCLUSIONS

Exercise performed between 15 and 14 h before a meal of moderate fat content reduced postprandial lipemia, mainly by lowering fasting triacylglycerols. The effect of exercise on postprandial triacylglycerol metabolism may be mediated, at least in part, by attenuated release of dietary fat from the intestine.

Ethanol with a mixed meal decreases the incretin levels early postprandially and increases postprandial lipemia in type 2 diabetic patients

Increased postprandial lipemia is a risk marker of cardiovascular disease (CVD). While moderate alcohol drinking is associated with a reduced risk of CVD in nondiabetic and type 2 diabetic patients, it is also known that alcohol increases postprandial triacylglycerol levels. The incretins, glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1), are important hormones from the gut that enhance nutrient-stimulated insulin secretion. Their responses to a moderate alcohol dose in type 2 diabetes have not previously been studied. We sought to determine how alcohol influences postprandial lipid and incretin levels in patients with type 2 diabetes when taken in combination with a fat-rich mixed meal. Eleven patients with type 2 diabetes ingested on 3 separate days in random order 3 different meals containing: 100 g butter alone or 100 g butter in combination with 40 g alcohol and 50 g carbohydrate, or 100 g butter and 120 g carbohydrate. The meal with alcohol and 50 g carbohydrate was isocaloric to that of 120 g carbohydrate. Triacylglycerol levels were measured after separation by ultracentrifugation into a chylomicron-rich fraction with Svedberg flotation unit values (Sf) > 1,000, and a chylomicron-poor fraction with Sf < 1,000. Supplementation of a fat-rich mixed meal with alcohol in type 2 diabetic subjects suppressed GLP-1 early in the postprandial phase and increased the late triacylglycerol responses compared with the 2 other meals. In the chylomicron-rich fraction, both triacylglycerol and cholesterol were increased by alcohol. No significant differences in high-density lipoprotein (HDL)-cholesterol levels were seen. Isocaloric amounts of carbohydrate and alcohol suppressed equally the postprandial free fatty acid levels, but carbohydrate increased the postprandial glucose, GIP, and insulin levels the most. Early in the postprandial phase, alcohol suppresses the incretin responses and increases the late postprandial triacylglycerol levels in type 2 diabetic patients. Whether this reflects an alcohol-induced suppression of the incretin response, which adds to the alcohol-induced impairment of triacylglycerol clearance in type 2 diabetic patients, remains to be elucidated.

Endogenous cholesterol synthesis is associated with VLDL-2 apoB-100 production in healthy humans

Subjects with high plasma cholesterol levels exhibit a high production of VLDL apolipoprotein B-100 (apoB-100), suggesting that cholesterol is a mediator for VLDL production. The objective of the study was to examine whether endogenous cholesterol synthesis, reflected by the lathosterol-cholesterol ratio (L-C ratio), affects the secretory rates of different VLDL subfractions. Ten healthy subjects were studied after overnight fasting. During a 10 h primed, constant infusion of 13C-valine (15 micromol/kg/h), enrichment was determined in apoB-100 from ultracentrifugally isolated VLDL-1 and VLDL-2 by gas chromatography mass spectrometry. The synthesis rates of VLDL-1 apoB-100 and VLDL-2 apoB-100, catabolism, and transfer were estimated by compartmental analysis. Mean VLDL-1 apoB-100 pool size was 90 +/- 15 mg, and mean VLDL-2 apoB-100 pool size was 111 +/- 14 mg. Absolute synthesis rate of VLDL-1 apoB-100 was 649 +/- 127 mg/day and 353 +/- 59 mg/day for VLDL-2 apoB-100. There was a strong association between the absolute synthesis rate of VLDL-2 apoB-100 and L-C ratio (r 2 = 0.61, P < 0.01). In contrast, no correlation was observed between L-C ratio and absolute synthesis rate of VLDL-1 apoB-100 (r 2 = 0.302, P = 0.09). In conclusion, these data provide additional support for an independent regulation of VLDL-1 apoB-100 and VLDL-2 apoB-100 production. Endogenous cholesterol synthesis is correlated only with the VLDL-2 apoB-100 production.

Protective effects of curcumin and photo-irradiated curcumin on circulatory lipids and lipid peroxidation products in alcohol and polyunsaturated fatty acid-induced toxicity

Alcohol is a neurotoxin associated with significant morbidity and mortality. Ethanol is found to induce a dose dependent increase in lipid peroxidation (LPO). The elevation in lipid peroxidative products and the loss of antioxidant defense potential are enhanced when alcohol is taken along with polyunsaturated fatty acid (PUFA) or heated PUFA. The present study was undertaken to evaluate the effects of curcumin and photo-irradiated curcumin on alcohol and PUFA induced LPO and lipid pro fi les in plasma. The levels of vitamin C and E were decreased significantly in alcohol + raw as well as heated PUFA groups. The treatment with curcumin and photo-irradiated curcumin (IC) increased their levels significantly. The increase was more significant in the IC group than the curcumin group. The levels of cholesterol, phospholipids (PL), triglycerides (TG), free fatty acids (FFA), thiobarbituric acid reactive substances (TBARS) and hydroperoxides (HP) were increased significantly in alcohol + raw as well as heated PUFA groups and the treatment with curcumin and IC, brought back the levels. But the IC reduced the levels more significantly than curcumin. Thus, our results indicate that IC is a more potent antioxidant than curcumin.

Comparative effects of curcumin and photo-irradiated curcumin on alcohol- and polyunsaturated fatty acid-induced hyperlipidemia

It is a known fact that ethanol increases lipid levels in humans and experimental animals. Reports show that the increased intake of polyunsaturated fatty acids (PUFAs) along with alcohol produces various pathological changes in liver resulting in hyperlipidemia. Heating of oil rich in PUFA produces various lipid peroxidative end products, which aggravate the pathological changes. In the present study, we have investigated the effect of curcumin (C) and photo-irradiated curcumin (IC) on alcohol- and PUFA-induced hyperlipidemia. Our results showed that the activities of alkaline phosphatase (ALP), gamma-glutamyl transferase (GGT) in plasma and levels of cholesterol, triglycerides (TGs) and free fatty acids (FFAs) in tissues were increased significantly in both alcohol + raw as well as heated PUFA groups compared to normal, but decreased significantly on treatment with curcumin and IC. The IC treatment decreased the levels more significantly compared to curcumin. The phospholipids (PLs) were increased significantly in heart and intestine and decreased in liver and kidney in both alcohol + raw as well as heated PUFA groups. The levels were significantly decreased in liver and kidney and increased in intestine and heart in both curcumin- and IC-treated groups. But the effect of IC was more pronounced than curcumin. Histopathological observations were also in correlation with the biochemical parameters. Thus, photo-irradiated curcumin proves itself to be more effective than curcumin in treating the above pathological conditions.

Effect of alcohol on lipids and lipoproteins in relation to atherosclerosis

Several studies indicate that light-to-moderate alcohol consumption is associated with a low prevalence of coronary heart disease. An increase in high-density lipoprotein (HDL) cholesterol is associated with alcohol intake and appears to account for approximately half of alcohol's cardioprotective effect. In addition to changes in the concentration and composition of lipoproteins, alcohol consumption may alter the activities of plasma proteins and enzymes involved in lipoprotein metabolism: cholesteryl ester transfer protein, phospholipid transfer protein, lecithin:cholesterol acyltransferase, lipoprotein lipase, hepatic lipase, paraoxonase-1 and phospholipases. Alcohol intake also results in modifications of lipoprotein particles: low sialic acid content in apolipoprotein components of lipoprotein particles (e.g., HDL apo E and apo J) and acetaldehyde modification of apolipoproteins. In addition, "abnormal" lipids, phosphatidylethanol, and fatty acid ethyl esters formed in the presence of ethanol are associated with lipoproteins in plasma. The effects of lipoproteins on the vascular wall cells (endothelial cells, smooth muscle cells, and monocyte/macrophages) may be modulated by ethanol and the alterations further enhanced by modified lipids. The present review discusses the effects of alcohol on lipoproteins in cholesterol transport, as well as the novel effects of lipoproteins on vascular wall cells.

Insulin stimulation of hepatic triacylglycerol secretion in the insulin-replete state: implications for the etiology of peripheral insulin resistance

Observations on humans, on rats in vivo, and on isolated perfused rat livers indicate that insulin stimulates hepatic very-low-density lipoprotein (VLDL)-TAG secretion when the liver is chronically exposed to the hormone. They suggest that frequent stimulation of insulin secretion throughout the diurnal cycle may result in a chronic stimulation of VLDL secretion and increased delivery of acyl moieties to the periphery, particularly to muscle, the most important site of insulin-sensitive glucose disposal. If acyl groups are provided in excess of the oxidative needs of the tissue, this may lead to induction of insulin resistance, irrespective of whether obesity is established concomitantly. Dietary factors that stimulate hepatic VLDL secretion may have the same effect and contribute to the induction of a vicious spiral leading to the development of the full-blown Metabolic Syndrome and its pathological consequences, including type-2 diabetes, stroke, and cardiovascular disease.

Recent findings in the study of postprandial lipemia

The study of postprandial metabolism is in the early stages compared with other areas of atherosclerosis research. Recent advances in postprandial research have included improvements in methodology and the investigation of factors that modulate the lipemic response to a meal. Enough studies have now been performed that normal ranges have been identified for blood triacylglycerol (TAG) concentrations that occur after a healthy patient consumes a standardized-mixed meal or a high-fat shake designed to elicit lipemia. Typical postprandial concentrations of other metabolites, such as apolipoproteins B48 and B100 or gastrointestinal hormones (eg, cholecystokinin), have not been studied sufficiently to be able to qualify what represents a standard postprandial response. The method of data analysis is also a key point to consider. Data from children are now becoming available, and the specific effects of ethnicity have just begun to be explored. New areas of study include the effects of different fatty acids (monosaturates or polyunsaturates), the sources of chylomicron lipids (dietary TAG and cholesterol versus that newly synthesized in the body), and the effects of alcoholic beverages consumed with the meal. Variables that can also affect the results of a meal test are under investigation. These include the type of food that is consumed the day before the meal test, the time of day the test is performed, and the palatability of the food. Given solid evidence that delayed postprandial lipemia is an independent risk factor for coronary heart disease, future scientific investigation in the area of postprandial metabolism is likely to yield discoveries that will significantly contribute to advancements in disease treatment.

Postprandial lipid handling

The etiological importance of postprandial lipid metabolism in the development of coronary artery disease is now well established. Since then, the work of Patsch and others has helped to establish the etiological importance of postprandial lipid metabolism in the development of coronary artery disease. Dietary and pharmacological interventions have been shown to produce dramatic improvement in postprandial lipid handling in high risk groups and have potential to prevent coronary artery disease through these effects. Research effort continues to focus on the complex mechanisms which underlie defects in postprandial lipid handling, with a view to understanding how lifestyle variables such as diet can be modified to prevent coronary artery disease.