A 90-day repeated-dose toxicity study of dietary alpha linolenic acid-enriched diacylglycerol oil in rats.

Diets supplemented with alpha-linolenic acid (ALA)-enriched diacylglycerol (DAG) oil-which mainly consists of oleic and linolenic, linoleic acids-have potential health benefits in terms of preventing or managing obesity. Although safety of DAG oil has been extensively investigated, toxicity of ALA-DAG oil has not been well understood. Hence, the present study was conducted to clarify the potential adverse effects, if any, of ALA-DAG oil in rats (10/sex/group) fed diets containing 1.375%, 2.75%, or 5.5% ALA-DAG oil for 90 days. Compared to control rats fed rapeseed oil or ALA-triacylglycerol oil (flaxseed oil), rats receiving ALA-DAG oil did not reveal any toxicologically significant treatment-related changes as evaluated by clinical signs, functional observational battery, body weight, food consumption, ophthalmology, urinalysis, hematology, clinical chemistry, organ weight, necropsy and histopathology. The no observed adverse effect levels for dietary exposure to ALA-DAG oil for male and female rats were 2916 and 3326 mg/kg body weight/day, respectively, the highest dose tested. The findings from this study suggest that consumption of ALA-DAG oil is unlikely to cause adverse effects.

Unavailability of liver triacylglycerol increases serum cholesterol concentration induced by dietary cholesterol in exogenously hypercholesterolemic (ExHC) rats.

BACKGROUND: Exogenously hypercholesterolemic (ExHC) rats develop hypercholesterolemia and low hepatic triacylglycerol (TAG) levels when dietary cholesterol is loaded. The responsible gene Smek2 was identified via linkage analysis using the original strain Sprague-Dawley (SD) rats. In this study, we compared SD and ExHC rats to investigate a relationship between hypercholesterolemia and the low hepatic TAG levels observed in ExHC rats. METHODS: Male 4-weeks-old ExHC and SD rats were fed a 1% cholesterol diet for 1 week. Serum and liver parameters were analyzed. Gene expression and enzyme activities related to TAG metabolism were also assessed. RESULTS: We reproducibly observed higher serum cholesterol and lower hepatic TAG levels in ExHC rats than in SD rats. Golgi apparatus in the livers of ExHC rats secreted ß-very-low-density lipoprotein (ß-VLDL) that had higher cholesterol ester (CE) and lower TAG content than those in the ß-VLDL secreted by SD rats. Gene expression related to fatty acid and TAG synthesis in ExHC rats was lower than that in SD rats. Enzymatic activities for fatty acid synthesis were also relatively lower in ExHC rats. Moreover, the fatty acid composition of hepatic and serum CE in ExHC rats showed that these CEs were not modified after secretion from the liver despite the similar activities of serum lecithin-cholesterol acyltransferase (LCAT) in ExHC rats to those in SD rats. CONCLUSIONS: Low production of liver TAG and secretion of CE-rich, TAG-poor ß-VLDL without modification by LCAT in the circulation contributed to hypercholesterolemia induced by dietary cholesterol in ExHC rats.

Genotoxicity studies of glycidol fatty acid ester (glycidol linoleate) and glycidol.

Glycidol fatty acid esters (GEs) are found in refined edible oils. Safety concerns have been alleged due to the possible release of glycidol (G), an animal carcinogen. We evaluated the genotoxic potential of glycidol linoleate (GL), a primary GE found in an edible oil (diacylglycerol oil), and G, using three established genotoxicity tests (a bacterial reverse mutation test, an in vitro chromosomal aberration test, and an in vivo bone marrow micronucleus test) under GLP conditions complying with all OECD guidelines. In the bacterial reverse mutation test, GL and G showed positive responses. The positive responses of GL were less than those of G and observed only in strains detecting point mutations where G showed remarkably positive responses. G was involved in the positive response of GL. In the chromosomal aberration test, GL did not induce chromosome aberrations whereas G induced structural chromosome aberrations in the presence and absence of metabolic activation. In the bone marrow micronucleus test, neither GL nor G induced significant increases of micronucleated immature (polychromatic) erythrocytes in bone marrow of test animals. Based on the above results as well as pertinent information on toxicokinetics, GL itself does not play a key role in genotoxic action.

Size-based distributions of postprandial lipoproteins in lymph and serum after oral administration of triacylglycerol and diacylglycerol oils in rats.

Several studies in humans and rodents suggest that postprandial serum triglyceride (TG) levels are decreased by a single oral administration of diacylglycerol (DAG) oil compared with administration of control triacylglycerol (TAG) oil. To gain further insight into the mechanisms underlying the metabolic properties of DAG in a postprandial state, we analyzed the size-based distributions of postprandial lipoproteins in the lymph and serum using gel filtration-based high-performance liquid chromatography. In thoracic duct lymph pooled for 3 h after oral administration of TAG or DAG, the size-based distributions of postprandial lymphatic lipoprotein-TG and -cholesterol levels did not differ significantly, suggesting that DAG did not affect the size of lipoprotein particles secreted from the small intestine. Serum lipoprotein-TG (60%) and -cholesterol levels (90%), however, were significantly different among fractions with a diameter of greater than 80 nm 1 to 2 h after the administration of DAG compared to TAG. In addition, there was a considerable, but nonsignificant, reduction in lipoprotein-TG levels (approximately 40%) in fractions with a diameter of 80 to 30 nm, suggesting that DAG-derived chylomicrons as well as DAG-derived chylomicron remnants were catabolized rapidly. In conclusion, dietary DAG reduced the amount of large-size lipoproteins in the serum, but did not affect the size distribution of lipoproteins produced in the small intestine. Thus, compared with TAG, dietary DAG may reduce the postprandial serum total TG levels.

Lymphatic absorption and deposition of various plant sterols in stroke-prone spontaneously hypertensive rats, a strain having a mutation in ATP binding cassette transporter G5.

ATP binding cassette transporter G5 (ABCG5) and ATP binding cassette transporter G8 (ABCG8) have been suggested to transport absorbed plant sterols and cholesterol from enterocytes to the intestinal lumen and from hepatocytes to bile. It has been thought that mutations of ABCG5 or ABCG8 cause the deposition of plant sterols in the body. In the present study, lymphatic absorption of various plant sterols and their deposition in various tissues was investigated in stroke-prone spontaneously hypertensive rats (SHRSP), having a mutation in Abcg5 and depositing plant sterols in the body. The order of lymphatic 24-h recovery of plant sterols was as follows: campesterol > sitosterol > brassicasterol > stigmasterol = sitostanol. When SHRSP were fed a diet containing one of the plant sterols, the depositions of campesterol and sitosterol were comparatively higher than those of brassicasterol, stigmasterol and sitostanol. Highly positive correlations were obtained between lymphatic recovery of plant sterols and their levels in plasma, liver, adipose tissue and heart. The tendency of differential absorption of plant sterols to the lymph in SHRSP was similar to that in normal Wistar rats previously reported by us (Hamada et al. Lipids 41:551-556, 2006). These observations suggest that differential absorption of various plant sterols is kept in SHRSP in spite of a mutation in Abcg5.

Dietary diacylglycerol reduces postprandial hyperlipidemia and ameliorates glucose intolerance in Otsuka Long-Evans Tokushima Fatty (OLETF) rats.

OBJECTIVE: The aim of the present study was to determine the effects of dietary diacylglycerol (DG) on the metabolism of lipids and glucose in type II diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats. METHODS: In experiment 1, the rats were orally administered 10 mL/kg of a triacylglycerol (TG) or DG emulsion (15% [w/v] oil), and the subsequent changes in the serum lipid levels were compared. In experiment 2, the rats were fed diets containing 15% DG or TG oil. After 22 weeks, the serum levels of lipids, glucose, and cytokines were determined. In addition, an oral glucose tolerance test (OGTT) was performed on the rats. RESULTS: Administration of an oral fat load caused marked hypertriglyceridemia with a peak at 2 h. Oral DG loading reduced the serum TG increase; the difference between the groups was significant at 4 and 6 h (P < 0.05). Diacylglycerol also markedly reduced the serum free fatty acid concentration increase due to the fat load. After 22 weeks of feeding, dietary DG reduced serum TG levels in the non-fasting state. Moreover, an OGTT revealed enhanced glucose disposal in the DG-fed rats compared with the TG-fed rats. Serum levels of adiponectin, an important insulin-sensitizing adipocytokine, were higher in the DG-fed rats than in the TG-fed rats (P < 0.05). In addition, DG-feeding reduced serum levels of C-reactive protein, a cardiovascular risk factor (P < 0.05). CONCLUSION: These results suggested that dietary DG improves lipid metabolism and glucose tolerance, and retards the progress of diabetes mellitus in OLETF rats.

Lymphatic absorption of structured triacylglycerols, 1(3)-stearoyl-2,3 (1)-dilinoleoylglycerol and 2-linoleoyl-1,3-distearoylglycerol in rats.

Lymphatic recovery of 1(3)-stearoyl-2,3(1)-dilinoleoylglycerol (SLL) and 2-linoleoyl-1,3-distearoylglycerol (SLS) which had been enzymatically synthesized were compared with those of trilinoleoylglycerol (LLL) and the randomly esterified triacylglycerol which contained stearic acid and linoleic acid at 1:2. Recoveries of linoleic acid in all of the triacylglycerols were more than 94.0%. Lymphatic 24 h-recoveries of stearic acid given as SLL and SLS were significantly lower than that of stearic acid given as the randomly esterified triacylglycerol. Recoveries of stearic acid from SLL, SLS and the randomly esterified triacylglycerol were 88.49%, 68.3% and 101%. respectively.

Comparison of the lymphatic transport of radiolabeled 1,3-dioleoylglycerol and trioleoylglycerol in rats.

It has been reported that, compared with TAG, DAG suppresses postprandial hypertriacylglycerolemia and reduces visceral fat levels in experimental animals and humans. To clarify the mechanism responsible for these beneficial effects, we compared the lymphatic transport of 1,3-DAG, a major isomer of DAG, and TAG in rats. Male SD rats, after insertion of a cannula into the thoracic duct, were given 1,3-di[1-14C]oleoylglycerol or tri[1-14C]oleoylglycerol via a stomach tube. The 24-h recovery of the radioactivity from 1,3-di[14C]oleoylglycerol in the lymph was slightly but significantly lower than that from tri[14C]oleoylglycerol (81.3+/-1.0 vs. 86.5+/-1.2%, respectively). However, in the first 1-h interval after administration, the recovery of radioactivity from 1,3-dioleoylglycerol was almost half of that from trioleoylglycerol (17.5+/-2.0 vs. 31.1+/-1.4%). The amount of TAG and phospholipids secreted into the lymph was significantly lower 1 h after the administration of 1,3-dioleoylglycerol compared with that after the administration of trioleoylglycerol. More than 90% of the radioactivity recovered in the lymph in the first 3 h was distributed in the TAG fraction for both 1,3-dioleoylglycerol and trioleoylglycerol. These results suggest that slower lymphatic transport of 1,3-DAG compared with TAG could be a factor in the suppression of postprandial hypertriacylglycerolemia. The possibility that the slower lymphatic transport of DAG contributes to the anti-obesity action observed in the feeding of 1,3-DAG cannot be excluded.