Dynamic Metabolome Analysis Reveals the Metabolic Fate of Medium-Chain Fatty Acids in AML12 Cells.

Several studies in hepatocyte cell lines reported that medium-chain fatty acids (MCFAs) with 6-12 carbons showed different metabolic properties from long-chain fatty acids (LCFAs). However, these studies reported unclear effects of different fatty acid molecules on hepatocyte metabolism. This study is aimed to capture the metabolic kinetics of MCFA assimilation in AML12 cells treated with octanoic acid (FA 8:0), decanoic acid (FA 10:0), or lauric acid (FA12:0) [LCFA; oleic acid (FA 18:1)] via metabolic profiling and dynamic metabolome analysis with 13C-labeling. The concentrations of total ketone bodies in the media of cells treated with FA 8:0 or FA 10:0 were 3.22- or 3.69-fold higher than those obtained with FA 18:1 treatment, respectively. FA 12:0 treatment did not significantly increase ketone body levels compared to DMSO treatment (control), whereas FA 12:0 treatment increased intracellular triacylglycerol (TG) levels 15.4 times compared to the control. Metabolic profiles of FA 12:0-treated samples differed from those of the FA 8:0-treated and FA 10:0-treated samples, suggesting that metabolic assimilation of MCFAs differed significantly depending on the MCFA type. Furthermore, the dynamic metabolome analysis clearly revealed that FA 8:0 was rapidly and quantitatively oxidized to acetyl-CoA and assimilated into ketone bodies, citrate cycle intermediates, and glucogenic amino acids but not readily into TGs.

Alpha-linolenic acid-rich flaxseed oil ingestion increases plasma adiponectin level in rats.

Adiponectin, an adipose-specific secretory protein, exhibits antidiabetic and antiatherogenic properties. The effect of alpha-linolenic acid (ALA) on adiponectin has not been revealed. ALA is included abundantly in vegetable oils such as flaxseed oil. In this study, we attempted to clarify the effect of ALA-rich flaxseed oil (FSO) intake on the adiponectin level in rats. Seven-week-old male Sprague-Dawley rats were fed test diets containing high oleic safflower oil (HOSO) or FSO for 4 weeks. After the experimental period, the plasma adiponectin concentration in the FSO-fed group was higher than that in the HOSO-fed group. The adiponectin content of perirenal adipose tissue in the FSO-fed group was also significantly higher than that in the HOSO-fed group. However, the adiponectin mRNA level in the perirenal adipose tissue did not differ significantly between the HOSO-fed and FSO-fed groups. In this study, we clarified the effect of the ALA-rich FSO ingestion on the plasma adiponectin concentration in rats. It was suggested that the ALA-rich FSO intake might exhibit beneficial effects through an increase of the adiponectin level.

Dietary soybean phospholipids increase the oxidative stability of lipids extracted from fish fillets.

We previously reported that the feeding of soybean phospholipids to fish increased the storage stability of n-3 polyunsaturated fatty acids (PUFA)-rich fish fillets. In this study, we examined the storage stability of lipids extracted from fish fed a diet containing soybean phospholipids and fish oil. Rainbow trout were divided into two groups, and were fed an either 2.5% soybean phospholipids (test) or no phospholipids (control) containing diet for 4 weeks. Lipids were extracted from fish fillets after the feeding period, and were subjected to an oxidation test. Lipids extracted from the fillets of fish in the test group exhibited lower values of oxygen absorption than those in the control group, and the degradation of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) was inhibited. Higher percentages of DHA and EPA were bound to phosphatidylcholine and phosphatidylethanolamine in the extracted lipids in the test group than in the control group. These results indicate that the oxidative stability of lipids extracted from fish fed soybean phospholipids is high, and that the higher percentages of DHA and EPA in PC and PE may have resulted in the higher stability of the lipids extracted from fish fillet.

Characterization of glutamate decarboxylase mediating gamma-amino butyric acid increase in the early germination stage of soybean (Glycine max [L.] Merr).

Glutamate decarboxylase (GAD) is an enzyme that catalyzes the production of gamma-amino butyric acid (GABA) from glutamate through a decarboxylation reaction. A full-length cDNA encoding glutamate decarboxylase (GmGAD1) was isolated from germinating soybean seeds (Glycine max [L.] Merr.). The GmGAD1 gene had a 1512-bp open reading frame, which encodes 503 amino acids. According to its sequence similarity with other GAD genes, GmGAD1 was classified into GAD1 in the plant GAD family. Recombinant GmGAD1 protein expressed in E. coli catalyzed alpha-decarboxylation of glutamic acid. The levels of GABA were rapidly increased in soybean seeds during the early imbibition period (6 h) of germination or during the soaking treatment, whereas mRNA of GmGAD1 gene was not detected in these materials. The GmGAD1 protein was observed in seeds of various states such as developing, matured and soaking. These data suggest that the increased levels of GABA during the early stage of germination or soaking treatment were mediated by GmGAD1 protein synthesized in developing soybean seeds.

Effect of life-long dietary n-6/n-3 fatty acid ratio on life span, serum lipids and serum glucose in Wistar rats.

Types of dietary lipid affect the life span of rats. In this study, we investigated the influence of the life-long dietary n-6/n-3 ratio on life span and serum lipid and glucose levels. A semi-purified diet adjusted to a constant saturated : monounsaturated : polyunsaturated fatty acid ratio and an n-6/n-3 ratio of 1 (R1), 4 (R4) or 16 (R16) was fed to rats (n=33) from 4 wk of age until death. There were no significant differences in the food intake or body weight, nor were there survival curve or mean life span variations among the 3 groups. The serum cholesterol levels after feeding the test diet for 6 and 12 mo were significantly lower in the R1 group than in the other groups, and the serum triacylglycerol levels were significantly lower than those in the R16 group. However, no significant differences were noted in the serum cholesterol or triacylglycerol level after feeding for 18 mo among the 3 groups. A significantly higher serum glucose level was noted in the R1 group only at 18 mo of test diet ingestion, compared to that in the R4 group. The results suggest that the influence of the dietary n-6/n-3 ratio on the serum lipid and glucose levels varies, depending on the duration and life stage of feeding. Our findings further suggest that the life span of Wistar rats is not affected even if the ratio of dietary n-6/n-3 changes from 1 to 16.

Effect of dietary n-6/n-3 ratio on liver n-6/n-3 ratio and peroxisomal beta-oxidation activity in rats.

The optimal dietary n-6/n-3 ratio has not been fully elucidated. To investigate the influence of the dietary n-6/n-3 ratio on this ratio in the body and on liver beta-oxidation peroxisomal activity, rats were fed diets containing fat at an n-6/n-3 ratio of 1 to 16 for 4 weeks. To investigate whether elevation of the liver peroxisomal beta-oxidation activity increases the n-6/n-3 ratio in the body, rats were fed a diet containing a peroxisome-activating agent, bezafibrate, for 2 weeks, and its influence on the liver n-6/n-3 ratio was examined. The slope of the regression line between the dietary and liver total lipid n-6/n-3 ratios was significantly smaller when the dietary n-6/n-3 ratio was 4 or greater than when it was smaller than 4. Peroxisomal beta-oxidation and acyl CoA oxidase activities were significantly lower in rats fed a diet with an n-6/n-3 ratio of 16 than in those fed a diet with a ratio of 1. The peroxisomal beta-oxidation activity in the bezafibrate-supplemented group was significantly higher than that in the control group. The serum and liver total lipid n-6/n-3 ratios were significantly higher in the 0.015% bezafibrate-supplemented group than in the control group. These findings suggest that the liver n-6/n-3 ratio might be controlled via peroxisomal beta-oxidation in rats.

Effect of dietary lard containing higher alpha-linolenic acid on plasma triacylglycerol in rats.

It is well known that the consumption of n-3 polyunsaturated fatty acid (PUFA) decreases the plasma triacylglycerol (TAG) level. The technology of elevating the content of n-3 PUFAs in pig meat has already reached a practical level. In this study, the effects of dietary lard containing higher alpha-linolenic acid (LNA) on plasma TAG were compared with those of normal lard in rats. The rats were fed a diet containing either 10% normal lard or a high linolenic lard for 4 weeks. The plasma and liver TAG levels in the high linolenic lard group were significantly lower than those in the normal lard group. The activity of the fatty acid synthase (FAS) of the liver in the high linolenic lard group was significantly lower than that in the normal lard group. The contents of n-3 PUFAs in hepatic total lipid, TAG fraction, and the phospholipids (PLs) fraction increased in the high linolenic lard group. The results indicate that the high linolenic lard suppressed hepatic FAS activity compared with the control lard, resulting in a lower concentration of plasma TAG. These results also suggest that pig meat containing high LNA may be more nourishing than normal pig meat.

Antihypertensive effect and safety of dietary alpha-linolenic acid in subjects with high-normal blood pressure and mild hypertension.

We investigated the antihypertensive effect and safety of alpha-linolenic acid (ALA) in human subjects. In Experiment 1, subjects with high-normal blood pressure and mild hypertension ingested bread containing 14 g of common blended oil (control oil) or ALA-enriched oil for 12 weeks. The test oil contained 2.6g/14 g of ALA. The subjects ingested strictly controlled meals during the study period. Systolic blood pressure was significantly lower in the ALA group than in the control group after ingestion of the test diet for 4, 8 and 12 weeks. Diastolic blood pressure was significantly lower in the ALA group than in the control group after ingestion of the test diet for 12 weeks. In Experiment 2, we evaluated the safety of high intake of ALA (7.8 g/d), particularly its effects on oxidation in the body and blood coagulation. Normotensive, high-normotensive and mildly hypertensive subjects ate bread that contained 42 g of the control oil or the test oil for 4 weeks. No significant difference was noted in the lipid peroxide level, high-sensitive C-reactive protein level, plasma prothrombin time or activated partial thromboplastin time between the two groups. No abnormal changes were noted after test diet ingestion on blood test or urinalysis, and no adverse event considered to have been induced by the test oil was observed in Experiment 1 and 2. These results suggest that ALA have an antihypertensive effect with no adverse effect in subjects with high-normal blood pressure and mild hypertension.