Effects of diacylglycerol on glucose, lipid metabolism, and plasma serotonin levels in lean Japanese

Postprandial Hyperlipidemia: Its Pathophysiology, Diagnosis, Atherogenesis, and Treatments

Postprandial hyperlipidemia showing postprandial increases in serum triglyceride (TG) is associated with the development of atherosclerotic cardiovascular disease (ASCVD). To diagnose postprandial hyperlipidemia, the oral fat loading test (OFLT) should be performed; however, this test is very time-consuming and is difficult to perform. Elevated serum TG levels reflect an increase in TG-rich lipoproteins (TRLs), such as chylomicrons (CM), very low-density lipoproteins (VLDL), and their remnants (CM remnants [CMRs] and VLDL remnants [VLDLRs]). Understanding of elevation in CMR and/or VLDLR can lead us to understand the existence of postprandial hyperlipidemia. The measurement of apo B48, which is a constituent of CM and CMR; non-fasting TG, which includes TG content in all lipoproteins including CM and CMR; non-high-density lipoprotein cholesterol (non-HDL-C), which includes TRLs and low-density lipoprotein; and remnant cholesterol are useful to reveal the existence of postprandial hyperlipidemia. Postprandial hyperlipidemia is observed in patients with familial type III hyperlipoproteinemia, familial combined hyperlipidemia, chronic kidney disease, metabolic syndrome and type 2 diabetes. Postprandial hyperlipidemia is closely related to postprandial hyperglycemia, and insulin resistance may be an inducing and enhancing factor for both postprandial hyperlipidemia and postprandial hyperglycemia. Remnant lipoproteins and metabolic disorders associated with postprandial hyperlipidemia have various atherogenic properties such as induction of inflammation and endothelial dysfunction. A healthy diet, calorie restriction, weight loss, and exercise positively impact postprandial hyperlipidemia. Anti-hyperlipidemic drugs such pemafibrate, fenofibrate, bezafibrate, ezetimibe, and eicosapentaenoic acid have been shown to improve postprandial hyperlipidemia. Anti-diabetic drugs including metformin, alpha-glucosidase inhibitors, pioglitazone, dipeptidyl-peptidase-4 inhibitors and glucagon-like peptide 1 analogues have been shown to ameliorate postprandial hyperlipidemia. Although sodium glucose cotransporter-2 inhibitors have not been proven to reduce postprandial hyperlipidemia, they reduced fasting apo B48 and remnant lipoprotein cholesterol. In conclusion, it is important to appropriately understand the existence of postprandial hyperlipidemia and to connect it to optimal treatments. However, there are some problems with the diagnosis for postprandial hyperlipidemia. Postprandial hyperlipidemia cannot be specifically defined by measures such as TG levels 2 h after a meal. To study interventions for postprandial hyperlipidemia with the outcome of preventing the onset of ASCVD, it is necessary to define postprandial hyperlipidemia using reference values such as IGT.

Oat Polar Lipids Improve Cardiometabolic-Related Markers after Breakfast and a Subsequent Standardized Lunch: A Randomized Crossover Study in Healthy Young Adults

It has been suggested that intake of polar lipids may beneficially modulate various metabolic variables. The purpose of this study was to evaluate the effect of oat polar lipids on postprandial and second meal glycemic regulation, blood lipids, gastrointestinal hormones, and subjective appetite-related variables in healthy humans. In a randomized design, twenty healthy subjects ingested four liquid cereal-based test beverages (42 g of available carbohydrates) containing: i. 30 g of oat oil with a low concentration (4%) of polar lipids (PLL), ii. 30 g of oat oil containing a high concentration (40%) of polar lipids (PLH), iii. 30 g of rapeseed oil (RSO), and iv. no added lipids (NL). The products were served as breakfast meals followed by a standardized lunch. Test variables were measured at fasting and during 3 h after breakfast and two additional hours following a standardized lunch. PLH reduced glucose and insulin responses after breakfast (0-120 min) compared to RSO, and after lunch (210-330 min) compared to RSO and PLL (p < 0.05). Compared to RSO, PLH resulted in increased concentrations of the gut hormones GLP-1 and PYY after the standardized lunch (p < 0.05). The results suggest that oat polar lipids have potential nutraceutical properties by modulating acute and second meal postprandial metabolic responses.

Diabetic dyslipidemia: evaluation and mechanism

Diabetes is one of the well-established independent risk factors for cardiovascular diseases. Diabetes induces dyslipidemia which is characterized by elevated fasting triglyceride (TG) and reduced high-density lipoprotein-cholesterol (HDL-C), and such diabetic dyslipidemia is a crucial determinant for atherogenesis and atherosclerotic progression in patients with diabetes. Previous measurement methods of lipoproteins have problems including time-consuming (ultracentrifugation) and inaccurate and impossible measurements of TG-rich lipoproteins such as chylomicron, intermediate-density lipoprotein (IDL) and very low-density lipoprotein (VLDL). Our developed anion-exchange high-performance liquid chromatography (AEX-HPLC) can measure all fractions of lipoproteins accurately. Our studies using AEX-HPLC showed that IDL and VLDL in type 2 diabetes were higher than non-diabetic subjects, and IDL and VLDL were higher in the order of type 2 diabetic patients with obesity, type 2 diabetic patients without obesity, and non-diabetic subjects. Here, we also describe the underlying mechanisms for development of diabetic dyslipidemia.

Metabolic and Hormonal Alterations with Diacylglycerol and Low Glycemic Index Starch during Canine Weight Loss

Obesity increases insulin resistance and disregulation of glucose homeostasis. This study investigated low glycemic index starch (LGIS)/diacylglycerol (DAG) diet on plasma insulin and circulating incretin hormones during canine weight loss. Obese Beagle dogs were fed one of four starch/oil combination diets (LGIS/DAG; LGIS/triacylglycerol (TAG); high glycemic index starch (HGIS)/DAG; and HGIS/TAG) for 9 weeks during the weight loss period. At weeks 1 and 8, fasting plasma insulin, glucose, nonesterified fatty acid (NEFA), glucose-dependent insulinotropic polypeptide (GIP), and glucagon-like peptide-1 (GLP-1) were determined. Weight loss did not affect fasting insulin, glucose, and NEFA, but fasting GIP increased and GLP-1 decreased. LGIS affected postprandial insulin at both times and glucose was similar to insulin, except 60 min postprandially with DAG at week 8. NEFA lowering was less with the LGIS diets initially but not thereafter. At 60 min postprandially on week 8, GIP was significantly elevated by DAG, while GLP-1 was increased only with the HD diet. LGIS suppressed insulin and glucose responses up to 180 min postprandially at both sample times. DAG increased incretin hormones as did the DAG/HGIS combination but only at week 8. This latter finding appeared to be related to the glucose response but not to insulin at 60 min.

Dietary 1-monoolein decreases postprandial GIP release by reducing jejunal transport of glucose and fatty acid in rodents

Postprandial secretion of insulin and glucose-dependent insulinotropic polypeptide (GIP) is differentially regulated by not only dietary carbohydrate but also fat. Recent studies have shown that the ingestion of diacylglycerol (DAG) results in lower postprandial insulin and GIP release than that of triacylglycerol (TAG), suggesting a possible mechanism for the antiobesity effect of DAG. The structural and metabolic characteristics of DAG are believed to be responsible for its beneficial effects. This study was designed to clarify the effect of 1-monoacylglycerol [oleic acid-rich (1-MO)], the characteristic metabolite of DAG, on postprandial insulin and GIP secretion, and the underlying mechanism. Dietary 1-MO dose dependently stimulated whole body fat utilization, and reduced high-fat diet-induced body weight gain and visceral fat accumulation in mice, both of which are consistent with the physiological effect of dietary DAG. Although glucose-stimulated insulin and GIP release was augmented by the addition of fat, coingestion of 1-MO reduced the postprandial hormone release in a dose-dependent manner. Either glucose or fatty acid transport into the everted intestinal sacs and enteroendocrine HuTu-80 cells was also reduced by the addition of 1-MO. Reduction of either glucose or fatty acid transport or the nutrient-stimulated GIP release by 1-MO was nullified when the intestine was pretreated with sodium-glucose cotransporter-1 (SGLT-1) or fatty acid translocase (FAT)/CD36 inhibitor. We conclude that dietary 1-MO attenuates postprandial GIP and insulin secretion by reducing the intestinal transport of the GIP secretagogues, which may be mediated via SGLT-1 and FAT/CD36. Reduced secretion of these anabolic hormones by 1-MO may be related to the antiobesity effect of DAG.

Food components with anti-obesity effect

Although many food components are reportedly beneficial to body-weight management, lack of understanding of molecular mechanisms and their function in overall adiposity under physiological conditions hinders successful and safe development of antiobesity functional foods. A positive energy balance resulting from an increase in food intake, a reduced energy expenditure, and/or dysfunction of adipose biology is associated with the development of obesity. This article provides an overview of the components involved in energy balance and adipose development and function. There is evidence that numerous ingredients found in foods can modulate energy balance and adipose biology, thereby potentially lowering adiposity.

Diacylglycerol oil reduces body fat but does not alter energy or lipid metabolism in overweight, hypertriglyceridemic women

Diacylglycerol (DAG) may undergo differential metabolism compared with triacylglycerol (TAG) in humans, possibly resulting in decreased serum TAG concentration and TAG synthesis and increased energy expenditure (EE), thus reducing fat accumulation. Our objective was to examine the efficacy of DAG oil (Enova oil) consumption on serum lipid profiles, hepatic lipogenesis, EE, and body weight and composition compared with a control oil-blend composed of sunflower, safflower, and rapeseed oils at a 1:1:1 ratio. Twenty-six overweight (78.3 +/- 3.6 kg body weight and BMI 30.0 +/- 0.7 kg/m(2)) mildly hypertriglyceridemic (1.81 +/- 0.66 mmol/L) women underwent 2 treatment phases of 28 d separated by a 4-wk washout period using a randomized crossover design. They consumed 40 g/d of either DAG or control oil during treatment phases. The baseline, EE, fat oxidation, body composition, and lipid profiles did not differ between the DAG and control oil intervention periods. Relative to control oil, DAG oil did not alter endpoint postprandial EE, fat oxidation, serum lipid profiles, or hepatic lipogenesis. However, DAG oil consumption reduced (P < 0.05) accumulation of body fat within trunk, android, and gynoid regions at the endpoint compared with control oil, although neither DAG nor control oil altered any of these variables during the 4-wk intervention period compared with their respective baseline levels. We conclude that although DAG oil is not effective in lowing serum lipids over a 4-wk intervention, it may be useful for reducing adiposity.

A molecular mechanism for diacylglycerol-mediated promotion of negative caloric balance

AIMS

A substitution of diacylglycerol (DAG) oil for triacylglycerol (TAG) oil in diet has been reported to reduce body fat and body weight, possibly by increasing postprandial energy expenditure (EE). We have previously studied plasma serotonin, which increases EE and exists in the small intestine, in individuals who ingested TAG and DAG oil, and found that DAG ingestion elevates plasma serotonin levels by about 50% compared with TAG ingestion. We studied the molecular mechanisms for DAG-mediated increase in serotonin and EE.

METHODS

We studied effects of 1-monoacylglycerol and 2-monoacylglycerol, distinct digestive products of DAG and TAG, respectively, on serotonin release from the Caco-2 cells (the human intestinal cell line, n = 8). Further, we studied effects of 1- and 2-monoacylglycerol, and serotonin on expression of mRNA associated with β-oxidation, FA metabolism, and thermogenesis, in the Caco-2 cells (n = 5).

RESULTS

1-monoacylglycerol (100 μM 1-monooleyl glycerol [1-MOG]) significantly increased serotonin release from the Caco-2 cells compared with 2-monoacylglycerol (100 μM 2-MOG) by 36.6%. Expression of mRNA of acyl-CoA oxidase (ACO), fatty acid translocase (FAT), and uncoupling protein-2 (UCP-2) were significantly higher in 100 μM 1-MOG-treated Caco-2 cells than 100 μM 2-MOG-treated cells by 12.8%, 23.7%, and 35.1%, respectively. Further, expression of mRNA of ACO, medium-chain acyl-CoA dehydrogenase, FAT, and UCP-2 were significantly elevated in serotonin (400 nM)-treated Caco-2 cells compared with cells incubated without serotonin by 28.7%, 30.1%, and 39.2%, respectively.

CONCLUSIONS

Our study demonstrated that 1-monoacylglycerol, a digestive product of DAG, increases serotonin release from the Caco-2 cells, and enhances expression of genes associated with β-oxidation, FA metabolism, and thermogenesis, and that serotonin increases expression of these genes, proposing a novel molecular mechanism for DAG-mediated promotion of negative caloric balance.

Coingestion of acylglycerols differentially affects glucose-induced insulin secretion via glucose-dependent insulinotropic polypeptide in C57BL/6J mice

The precise role of fat in postprandial glycemia and insulinemia has not been thoroughly researched because postprandial blood glucose and concurrent insulin secretion are largely assumed to be proportional to carbohydrate intake. Recent studies have suggested that dietary fat differentially regulates the postprandial insulin response. To explore this, we examined the effects of coadministered fat on glucose-induced glycemia and insulinemia in C57BL/6J mice. The insulin response to glucose was augmented by the addition of glycerol trioleate (TO) in a dose-dependent manner, which was associated with enhanced glucose transport from the circulation to muscle and adipose tissues. To investigate the mechanism underlying fat-induced hyperinsulinemia, we examined the release of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1. TO increased GIP secretion, whereas glucagon-like peptide-1 secretion was unaffected. TO-induced hyperinsulinemia was significantly attenuated by the pretreatment of mice with a specific GIP antagonist. Diacylglycerol (DAG) promoted lower postprandial GIP and triglyceride responses and, when ingested with glucose, a lower insulin response compared with triacylglycerol of a similar fatty acid composition. Pluronic L-81, an inhibitor of chylomicron formation, reduced not only the triglyceride response but also TO-induced GIP secretion, indicating that the lower GIP response after DAG ingestion may be associated with retarded chylomicron formation in the small intestine. We conclude that dietary fat augments glucose-induced insulinemia via gut-derived GIP and, thereby, influences postprandial nutrient metabolism in mice. DAG promotes a lower GIP and thereby reduced insulin responses compared with triacylglycerol, which may differentially influence postprandial energy homeostasis.

The effects of diacylglycerol oil on fat oxidation and energy expenditure in humans and animals

Studies in animals and humans indicate that diets containing diacylglycerol (DAG) oil (containing >80% DAG) decrease body weight gain and body fat accumulation, especially visceral fat. Body weight and body fat are controlled by energy expenditure, fat oxidation, fat storage capacity, and appetite control. Recent researches indicate that DAG oil, compared with conventional oils, has distinct metabolic effects. We review the evidence concerning the effects of DAG oil intake on fat oxidation and energy expenditure. In humans, dietary DAG is more susceptible to oxidation, and in animals 1,3-DAG, a major component of DAG oil, is rapidly oxidized. Short-term human studies with indirect calorimetry demonstrate greater fat oxidation with DAG oil consumption compared with triacylglycerol (TAG) oil consumption. Furthermore, DAG oil consumption for 14 days stimulates energy expenditure. Based on these reports, enhanced fat oxidation and energy expenditure by daily DAG oil intake could contribute to long-term reductions in body weight and fat accumulation. The literature provides support for the notion that dietary DAG is more rapidly oxidized than dietary TAG, and that, compared with TAG oil, DAG oil consumption increases whole body fat oxidation. The effects of DAG oil consumption on energy expenditure, however, remain inconclusive. (c) 2009 International Union of Biochemistry and Molecular Biology, Inc.