Effect of diacylglycerol on the development of impaired glucose tolerance in sucrose-fed rats

Exploring the fates and molecular changes of different diacylglycerol-rich lipids during in vitro digestion

This study aimed to support the pursuit of healthy oils and investigate the relationships between lipid compositions and digestion fates of diacylglycerol (DAG)-rich lipids using an in vitro digestion model. Soybean-, olive-, rapeseed-, camellia-, and linseed-based DAG-rich lipids (termed SD, OD, RD, CD, and LD, respectively) were selected. These lipids exhibited identical lipolysis degrees (92.20-94.36 %) and digestion rates (0.0403-0.0466 s^-1). The lipid structure (DAG or triacylglycerol) was a more important factor affecting the lipolysis degree than other indices (glycerolipid composition and fatty acid composition). For RD, CD and LD with similar fatty acid compositions, the same fatty acid had different release levels, probably due to their different glycerolipid compositions (causing different distributions of the fatty acid in UU-DAG, USa-DAG and SaSa-DAG; U: unsaturated fatty acids, Sa: saturated fatty acids). This study provides insights into the digestion behaviors of different DAG-rich lipids and supports their food or pharmaceutical applications.

Diacylglycerol levels modulate the cellular distribution of the nicotinic acetylcholine receptor

Diacylglycerol (DAG), a second messenger involved in different cell signaling cascades, activates protein kinase C (PKC) and D (PKD), among other kinases. The present work analyzes the effects resulting from the alteration of DAG levels on neuronal and muscle nicotinic acetylcholine receptor (AChR) distribution. We employ CHO-K1/A5 cells, expressing adult muscle-type AChR in a stable manner, and hippocampal neurons, which endogenously express various subtypes of neuronal AChR. CHO-K1/A5 cells treated with dioctanoylglycerol (DOG) for different periods showed augmented AChR cell surface levels at short incubation times (30min-4h) whereas at longer times (18h) the AChR was shifted to intracellular compartments. Similarly, in cultured hippocampal neurons surface AChR levels increased as a result of DOG incubation for 4h. Inhibition of endogenous DAG catabolism produced changes in AChR distribution similar to those induced by DOG treatment. Specific enzyme inhibitors and Western blot assays revealed that DAGs exert their effect on AChR distribution through the modulation of the activity of classical PKC (cPKC), novel PKC (nPKC) and PKD activity.

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.

Metabolic syndrome as a risk factor for neurological disorders

The metabolic syndrome is a cluster of common pathologies: abdominal obesity linked to an excess of visceral fat, insulin resistance, dyslipidemia and hypertension. At the molecular level, metabolic syndrome is accompanied not only by dysregulation in the expression of adipokines (cytokines and chemokines), but also by alterations in levels of leptin, a peptide hormone released by white adipose tissue. These changes modulate immune response and inflammation that lead to alterations in the hypothalamic 'bodyweight/appetite/satiety set point,' resulting in the initiation and development of metabolic syndrome. Metabolic syndrome is a risk factor for neurological disorders such as stroke, depression and Alzheimer's disease. The molecular mechanism underlying the mirror relationship between metabolic syndrome and neurological disorders is not fully understood. However, it is becoming increasingly evident that all cellular and biochemical alterations observed in metabolic syndrome like impairment of endothelial cell function, abnormality in essential fatty acid metabolism and alterations in lipid mediators along with abnormal insulin/leptin signaling may represent a pathological bridge between metabolic syndrome and neurological disorders such as stroke, Alzheimer's disease and depression. The purpose of this review is not only to describe the involvement of brain in the pathogenesis of metabolic syndrome, but also to link the pathogenesis of metabolic syndrome with neurochemical changes in stroke, Alzheimer's disease and depression to a wider audience of neuroscientists with the hope that this discussion will initiate more studies on the relationship between metabolic syndrome and neurological disorders.

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.

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

OBJECTIVE

Diacylglycerol (DAG)-rich oil has been suggested to suppress postprandial hyperlipidemia and promote negative caloric balance by increasing energy expenditure (EE), due to small intestine physiochemical dynamics that differ from triacylglycerol (TAG). We studied the effect of DAG on postprandial glucose/insulin metabolism by loading of carbohydrate with oil. Further, to reveal the mechanism for increased EE by DAG, we measured plasma serotonin, which is mostly present in the small intestine and mediates peripheral sympathetic thermogenesis.

METHODS AND PROCEDURES

Randomized crossover study with 2-week wash-out interval between differing fat ingestion. Seven male, lean, Japanese students ingested DAG or TAG oil with 40 g of carbohydrate. Measurements of metabolic parameters were performed before and at 2, 4, and 6 h after fat ingestion. Plasma serotonin levels and cholesterol concentration in each lipoprotein were measured using high-performance liquid chromatography (HPLC).

RESULTS

The substitution of DAG for TAG decreased very-low-density lipoprotein-cholesterol (VLDL-C) by 45.6% at 2 h, and decreased serum insulin by 41.3% at 4 h after ingestion. The incremental area under the curve (IAUC) for VLDL-C was positively correlated with the IAUC for insulin. Concurrently, DAG elevated plasma serotonin levels by 47.3% at 2 h, while TAG did not influence.

DISCUSSION

This study indicates that the substitution of DAG for TAG suppresses the postprandial increase in serum VLDL-C and insulin. This study also demonstrates that DAG ingestion increases plasma serotonin, proposing a possible mechanism for a postprandial increase in EE by DAG.

Diacylglycerol oil for the metabolic syndrome

Excess adiposity has been shown to play a crucial role in the development of the metabolic syndrome. The elevated fasting and postprandial triglyceride-rich lipoprotein levels is the central lipid abnormality observed in the metabolic syndrome. Recent studies have indicated that diacylglycerol (DAG) is effective for fasting and postprandial hyperlipidemia and preventing excess adiposity by increasing postprandial energy expenditure. We will here discuss the mechanisms of DAG-mediated improvements in hyperlipidemia and in postprandial energy expenditure, and effects of DAG oil on lipid/glucose metabolism and on body fat. Further, the therapeutic application of DAG for the metabolic syndrome will be considered.

Dietary 1,3-diacylglycerol protects against diet-induced obesity and insulin resistance

To investigate the effect of dietary 1,3-diacylglycerol (DAG) on the development of insulin resistance (IR) and obesity, brown adipose tissue-deficient mice, a model of high-fat diet-induced IR and obesity, were fed Western-type diets (WTD) containing either DAG oil (n = 8) or standard triacylglycerol (TAG) oil (n = 9) for 15 weeks, beginning at 8 weeks of age. Although brown adipose tissue-deficient mice became obese on both TAG- and DAG-enriched WTD (TAG-WTD and DAG-WTD), the mice eating DAG-WTD gained less weight and had less body fat accumulation. The results of glucose tolerance tests conducted after 5 weeks of each WTD were not different. However, after 10 weeks of each WTD, impaired glucose tolerance developed in the TAG-WTD group but was prevented by DAG-WTD. Exploratory analyses of gene expression suggested that consumption of DAG-WTD was associated with reduced phosphoenolpyruvate carboxykinase gene expression in liver and increased expression of the genes for peroxisome proliferator-activated receptor alpha, lipoprotein lipase, and uncoupling proteins 2 and 3 in skeletal muscle. There were no effects of the DAG-WTD on fasting and postprandial plasma triglyceride (TG) levels, hepatic TG content, or the rate of secretion of TG from the liver. These findings suggest that diets enriched in 1,3-DAG oil may reduce WTD-induced IR and body fat accumulation by suppressing gluconeogenesis in liver and stimulating fat oxidation in skeletal muscle.

Replacements for trans fats-will there be an oil shortage?

Manufacturers use the process of hydrogenation to create trans fats in order to increase the shelf life of baked and fried foods. Ingestion of trans fats is associated with an increased risk of cardiovascular disease. A groundswell of public sentiment is causing regulatory bodies to ban the use of trans fats in foods. Alternatives to trans fats are needed now in order to preserve the freshness and provide an appealing texture of many packaged foods. As trans fats become phased out, there are eight types of approaches currently being developed to substitute for these fats as ingredients for baked and fried foods: (1) modified hydrogenation, (2) genetically modified seeds, (3) interesterification, (4) fractionation and blending, (5) butter and animal fat, (6) natural saturated oils, (7) natural unsaturated oils, and (8) fat substitutes. These alternatives to trans fats will require close scrutiny to ascertain whether they will also turn out to be linked with cardiovascular disease.