Nobuya Shirai

Effect of season on the fatty acid composition and free amino acid content of the sardine Sardinops melanostictus.

The purpose of this study was to clarify the seasonal variation of fatty acid composition and free amino acid content in the Japanese sardine (Sardinops melanostictus) from the sea of Hyuga-Nada, and the relationship between the fatty acid composition of this sardine and that of plankton in the area. The lipid content of sardines at the sea of Hyuga-Nada was low in February (1.8%) and high (7.2%) from July to September. The major fatty acids in the total lipids from sardine were myristic acid (14:0), palmitic acid (16:0), stearic acid (18:0), palmitoleic acid (16:1 n-7), oleic acid (18:1 n-9), eicosapentaenoic acid (20:5 n-3), and docosahexaenoic acid (22:6 n-3). The characteristics of the fatty acids isolated from sardines in July were similar to those from plankton in the same season. This reflects the deposition of plankton fatty acids in sardine depot fat. The season of high free histidine content in the ordinary meat corresponded with that of high lipid content. These results suggested that both the fatty acid composition of sardines and the high concentrations of certain amino acids in free form are influenced by the intake and seasonal variation of composition of plankton.

Dietary and seasonal effects on the dorsal meat lipid composition of Japanese (Silurus asotus) and Thai catfish (Clarias macrocephalus and hybrid Clarias macrocephalus and Clarias galipinus)

The effects of dietary lipids and seasonal variation on the lipids of wild and cultured catfish (Japanese catfish, Silurus asotus; Thai catfish, Clarias macrocephalus and hybrid Clarias macrocephalus x Clarias galipinus) were determined by analysis of the lipid content and fatty acid composition of their dorsal meat. The predominant fatty acids of dorsal meat were 16:0, 18:1n-9, 18:2n-6, 20:4n-6 (arachidonic acid, AA), and 22:6n-3 (docosahexaenoic acid, DHA). The DHA content in the diet of Japanese catfish was higher than that in the diet of Thai catfish, and this was reflected in the dorsal meat of the Japanese catfish, which had a remarkably high percentage of DHA compared with the meat of the Thai catfish. Cultured Japanese catfish had a higher percentage of 18:2n-6 than Thai fish and a lower percentage of AA in winter than in summer season. There were also seasonal variations in the percentage of n-6 fatty acids in Japanese catfish. In summer, the fatty acid composition of the cultured Japanese catfish was similar to that of the wild catfish. These fatty acid changes in the lipid classes, triacylglycerol, phosphatidylcholine and phosphatidylethanolamine were similar to those observed for total lipids. These results indicate that the percentage of DHA in the dorsal meat of catfish is influenced by dietary fatty acid, and it may be that it can be increased in cultivated fish by administering a diet containing a large amount of DHA.

Spawning and season affect lipid content and fatty acid composition of ovary and liver in Japanese catfish (Silurus asotus)

The influences of spawning and season on lipid content, lipid classes, and fatty acid composition were assessed in ovary and liver of wild and cultured Japanese catfish (Silurus asotus). The lipid content (7.3+/-1.6 g/100 g wet wt.) of ovary from wild catfish at spawning was higher than that at post-spawn. However, no influence of spawning on the lipid content of liver was observed. Docosahexaenoic acid [DHA, C22:6(n-3)] in ovary lipids was 12.3+/-0.5% of total fatty acids. The percentage of n-7 monounsaturated fatty acids in triacylglycerol from the ovary and liver in the spawning season was high. Percentages of C22:6(n-3) in phosphatidylcholine and phosphatidylethanolamine from ovary were higher during spawning than after spawning. No significant differences were observed in the lipid content of ovary and liver from cultured catfish between seasons (summer vs. winter). Content of arachidonic acid (C20:4n-6) in ovary and liver from cultured catfish was higher in summer than in winter. There were differences in lipid classes of ovary and liver by spawning and season. These results suggest that the lipid metabolism in Japanese catfish is greatly influenced by spawning and season.

Effect of Dietary Docosahexaenoic Acid and Catechins on Maze Behavior in Mice

Background/Aims: Docosahexaenoic acid (DHA; 22:6 n–3) and catechins are food components that play an important role in maintaining human health. However, the effect of a simultaneous intake of DHA and catechins on brain function is unknown. The purpose of this study was to investigate the effect of DHA and catechins on maze behavior in mice. Method: Adult (5 months old) and old (15 months old) male mice were fed 5% lard diets containing 0 or 1.5% DHA ethyl ester (DHA-EE), either with or without 0.5% catechins, for 3.5 months. Maze behavior was assessed 3 months after the start of the feeding experiment. The time required and distance traveled to reach the maze exit, and the number of times that a mouse strayed into blind alleys in the maze were measured. The fatty acid compositions of plasma and brain lipids were measured after the maze behavior experiment. Results: Adult mice in the catechin, DHA-EE, and DHA-EE + catechin diet groups required less time and traveled a shorter distance to reach the maze exit, and strayed into blind alleys fewer times than those in the corresponding lard groups. Among old mice, the DHA-EE + catechin diet group showed an improvement in maze behavior. No marked differences in the brain fatty acid composition between lard and catechin diet groups were observed; in the DHA-EE intake groups, the brain DHA percentage was raised. Conclusion: These results suggest that a simultaneous intake of DHA and catechins may certainly enhance brain function in both adult and old mice.

Reduction in Plasma Glucose after Lipid Changes in Mice Fed Fish Oil, Docosahexaenoic Acid, and Eicosapentaenoic Acid Diets

Background/Aim: Effects of the dietary docosahexaenoic acid (DHA), eicosapentaenoic acid (EPA), and fish oil on weekly changes in plasma glucose, total cholesterol, triacylglycerol, and phospholipid concentrations of male Crlj:CD-1 mice were investigated. Method: Animals were fed five different experimental diets which contained 6.0% lard (lard diet), 6.0% fish oil (fish oil diet), 1.5% DHA-ethyl ester + 4.5% lard (DHA diet), 0.4% EPA-ethyl ester + 5.6% lard (EPA diet), and 1.5% DHA-ethyl ester + 0.4% EPA ethyl ester + 4.1% lard (DHA+EPA diet) for 17 weeks. Glucose and lipid concentrations in plasma collected at weeks 0, 1, 2, 4, 6, 8, 12, and 16 were measured. Results: Plasma phospholipid concentrations were significantly lower in mice fed the fish oil and DHA+EPA diets than in those fed the lard diet at week 2. Plasma total cholesterol and glucose concentrations were significantly lower in the fish oil diet group than in the lard diet group at weeks 6 and 8, respectively. Conclusion: These results indicate that the decreases in plasma glucose concentrations in response to intakes of DHA and EPA in mice take place over a longer period of time than similar decreases in the plasma lipid concentrations.

Effects of Western, Vegetarian, and Japanese Dietary Fat Model Diets with or without Green Tea Extract on the Plasma Lipids and Glucose, and Liver Lipids in Mice

Background/Aims: The purpose of this study was to investigate the long-term effects of three model diets containing different fats, with or without a small amount of green tea extract (GTE), on plasma lipids and glucose, and liver lipids in mice. Methods: Male mice (2 months old) fed 10% fat diets with Western (W), Vegetarian (V), and Japanese (J) fat compositions with or without 0.03% GTE for 7 months. Results: The concentrations of plasma and liver total cholesterol in animals fed the W diet were not significantly different from those fed the J diet. Plasma triacylglycerol (TG) concentrations were significantly different from one another in the following order: V > J > W diet groups. GTE supplementation significantly reduced plasma and liver TG content only in V diet group. Plasma glucose (Glu) concentrations were in the following order: W > V > J diet groups, and the GTE supplementation reduced the concentration of Glu in each diet group. The ratios of plasma n–6 to n–3 fatty acids were in the following order: V > W > J diet groups, regardless of GTE supplementation. Conclusion: These findings show the possibility that Japanese eating habits combined with drinking green tea might be a factor in preventing the onset of non-insulin-dependent diabetes mellitus.

Effect of Erabu Sea Snake (Laticauda semifasciata) Lipids on the Swimming Endurance of Mice

Background/Aim: This study was designed to investigate the effect of Erabu sea snake (Laticauda semifasciata) lipids on the swimming endurance of mice. Method: Twelve-week-old male Crlj: CD-1 (ICR) mice were fed one of three experimental diets containing 6% lard, fish oil or sea snake lipids for 16 weeks. Swimming exercise was conducted in an acrylic plastic tank filled with 25 cm of water maintained at 23°C. Every 4 weeks, the mice were made to perform swimming exercises with loads attached to their tails, corresponding to approximately 1 or 2% of their body weights. Results: The group fed the sea snake lipid diet exhibited significantly improved swimming endurance compared with the lard diet group (p < 0.05); however, this result was not observed in the fish oil diet group. In the sea snake lipid diet group, plasma and muscle lactates were significantly lower, and plasma glucose and muscle glycogen were significantly higher than in the lard diet group (p < 0.05). Conclusion: These results suggest that the intake of sea snake lipids enhanced the swimming endurance of the mice by delaying the accumulation of lactate during swimming exercise.

Effects of Simultaneous Intakes of Fish Oil and Green Tea Extracts on Plasma, Glucose, Insulin, C-Peptide, and Adiponectin and on Liver Lipid Concentrations in Mice Fed Low- and High-Fat Diets

Aims: The purpose of this study was to clarify the effects of a simultaneous intake of fish oil and green tea extracts (GTE) on plasma lipids, glucose (Glu), insulin, C-peptide, and adiponectin concentrations and on liver lipids in mice fed low- and high-fat diets. Methods: Male mice (5 months old) were fed low-fat (5%) or high-fat (20%) diets containing 0% (5 or 20% lard), 1% (4 or 19% lard) or 5% (0 or 15% lard) fish oil with or without 1% GTE for 3 months. Results: Single or combined intakes of fish oil and GTE intakes significantly lowered plasma and liver total cholesterol (T-chol) and triacylglycerol (TG) concentrations in mice on high-fat diets. However, a positive effect of GTE alone was not observed in the plasma T-chol and TG concentrations of mice on low-fat diets. Plasma Glu concentrations were significantly lowered by dietary fish oil in mice on the low- and high-fat diets. A tendency of GTE intake to decrease plasma Glu in mice on both the low- and high-fat diets was not significant. An intake of GTE only minimally influenced plasma insulin, C-peptide, and adiponectin concentrations, but fish oil supplementation increased the adiponectin concentration in mice on the low- and high-fat diets. GTE addition to the diets had no adverse effects on reductions by fish oil. Conclusion: These results suggest that a simultaneous intake of fish oil and GTE can improve plasma and liver lipid and plasma Glu profiles in mice fed a high-fat diet without any negative interactions of fish oil and GTE.

The effects of Erabu sea snake oil on the plasma lipids and glucose, and liver lipids in mice

Abstract The aims of this study were to determine the effects of Erabu sea snake Laticauda Semifasciata , a marine reptile, oil on plasma and liver lipids and plasma glucose in mice. Male mice (6 months old) were fed a diet containing 5% lard, 5% Erabu sea snake oil, or 5% fish oil mixture, which had the same percentage of docosahexaenoic acid as the Erabu sea snake oil, for 4 months. The plasma and liver total cholesterol, triacylglycerol and phospholipid concentrations, and plasma glucose concentrations were significantly lower in mice fed the sea snake oil diet than in those animals fed the lard diet. There were no significant differences in plasma and liver lipid components between the lard and fish oil mixture diet groups. There were no marked differences in plasma or liver fatty acid composition between the animals fed sea snake oil and those fed the fish oil mixture. These results indicate that a diet of Erabu sea snake oil has a lowering-effect on plasma and liver lipids and plasma glucose in mice and is more effective than a fish oil mixture.

Effects of simultaneous docosahexaenoic acid and catechin intakes on the plasma and liver lipids in low- and high-fat diet fed mice

The purpose of this study was to clarify the synergistic effects of fish oil and tea components on plasma and liver lipids in mice fed low- and high-fat diets. Male mice (5 months old) were fed for 4 months on low (5%) or high (20%) fat diets containing 0%, 0.1%, or 1% docosahexaenoic acid ethyl ester (DHA-EE) either with or without 0.03% catechin. The plasma total cholesterol (T-Chol) content of mice fed the 1% DHA-EE + 0.03% catechin diet was the lowest among the experimental low-fat diet groups. The plasma total and free cholesterol and phospholipids were significantly lower in the mice fed 1% DHA-EE + 0.03% catechin diet than in animals fed 1% DHA-EE or 0.03% catechin diets. However, there were no marked differences in the plasma and liver lipid components between any of the experimental high-fat diet groups. In mice fed either the low- or high-fat diet, plasma and liver DHA percentages rose with the increasing of DHA-EE supplementation, while the catchins supplementation hardly influenced the plasma and liver fatty acid composition. These results suggest that simultaneous intakes of DHA and catechins may be effective in the improving plasma lipid levels in animals fed low-fat diet.