Kanae Yamashita

Sesame seed and its lignans produce marked enhancement of vitamin E activity in rats fed a low α-tocopherol diet

Three series of experiments demonstrated that sesame seed and its lignans cause significant elevation of α-tocopherol content in rats. In Experiment 1, 20% sesame seed (with a negligible amount of α-tocopherol) supplementing 10 (low), 50 (normal), or 250 (high) mg/kg α-tocopherol diets (protein and fat concentrations in diets were adjusted to 200 and 110 g/kg, respectively) all caused a significant increase of α-tocopherol in the blood and tissue of rats. In Experiment 2, groups of rats were fed five different diets: a vitamin E-free control diet, a low α-tocopherol diet, and three low α-tocopherol diets supplemented with 5, 10, and 15% sesame seed. Changes in lipid peroxides in liver, red blood cell hemolysis, and pyruvate kinase activity, as indices of vitamin E deficiency, were examined. These indices were high in the low α-tocopherol diet, whereas supplementation with even 5% sesame seed suppressed these indices completely and caused a significant increase of α-tocopherol content in the plasma and liver. In Experiment 3 two diets containing sesame lignan (sesaminol or sesamin) and low α-tocopherol were tested. Results in both of the sesame lignan-fed groups were comparable to those observed in the sesame seed-fed groups as shown in Experiment 2. These experiments indicate that sesame seed lignans enhance vitamin E activity in rats fed a low α-tocopherol diet and cause a marked increase in α-tocopherol concentration in the blood and tissue of rats fed an α-tocopherol-containing diet with sesame seed or its lignans.

Comparative effects of flaxseed and sesame seed on vitamin E and cholesterol levels in rats

Flaxseed and sesame seed both contain more than 40% fat, about 20% protein, and vitamin E, mostly γ-tocopherol. Furthermore, both contain considerable amounts of plant lignans. However, flaxseed contains 54% α-linolenic acid, but sesame seed only 0.6%, and the chemical structures of flaxseed and sesame lignans are different. In this study, we investigated the differential effects of flaxseed and sesame seed on plasma and tissue γ-tocopherol, TBARS, and cholesterol concentrations. Rats were fed experimental diets for 4 wk: vitamin E-free, (-VE), γ-tocopherol, flaxseed (FS), sesame seed (SS), flaxseed oil (FO), FO with sesamin (FOS), and defatted flaxseed (DFF). SS and FOS diets induced significantly higher γ-tocopherol concentrations in plasma and liver compared with FS, FO, and DFF diets. Groups fed FS, FO, and FOS showed lower plasma total cholesterol compared with the SS and DFF groups. Higher TBARS concentrations in plasma and liver were observed in the FS and FO groups but not in the FOS groups. These results suggest that sesame seed and its lignans induced higher γ-tocopherol and lower TBARS concentrations, whereas flaxseed lignans had no such effects. Further, α-linolenic acid produced strong plasma cholesterol-lowering effects and higher TBARS concentrations.

Effects of various tocopherol-containing diets on tocopherol secretion into bile.

Abstractγ-Tocopherol is abundant in common vegetable oil, but its concentration in plasma and liver is much lower than that of α-tocopherol. Discrimination between different forms of tocopherol is thought to take placevia the hepatic α-tocopherol transfer protein (α-TTP). γ-Tocopherol, with a low binding capacity to α-TTP, is thought to be excretedvia the bile. Our previous studies showed that γ-tocopherol administered with sesame seed exhibits significantly higher concentrations in the plasma and liver of rats than γ-tocopherol alone. Thus, we attempted to confirm whether a much higher amount of γ-tocopherol rather than γ-tocopherol would be secreted in the bile, and whether sesame seed would suppress the secretion of γ-tocopherol. In one experiment, we examined the concentrations of α-or γ-tocopherol in the plasma, liver, and bile of rats fed diets containing 300 mg/kg of α-tocopherol, 300 mg/kg of γ-tocopherol, or 300 mg/kg each of α-tocopherol+γ-tocopherol, and in the other experiment, we compared the γ-tocopherol concentrations of rats fed a diet of γ-tocopherol alone to those of rats fed a γ-tocopherol+sesame seed diet (each diet contained 300 mg/kg γ-tocopherol). The bile collection was done over 6 h. The γ-tocopherol concentration in the bile was markedly lower than that of α-tocopherol, paralleling the concentrations in the plasma and liver. Intake of α-tocopherol and γ-tocopherol together further lowered the concentration of γ-tocopherol in the bile as well as in the plasma and liver, compared to the intake of γ-tocopherol alone. The γ-tocopherol concentration in the bile, as well as in the plasma and liver, was markedly higher in the sesame seed-fed group than in the γ-tocopherol alone group. We found that the concentrations of α- or γ-tocopherol in the bile showed a good correlation with the concentrations of α- or γ-tocopherol in the liver, though the concentrations in the bile were substantially lower than those in the liver. These findings suggest that secretion into the bile is not a major metabolic route of α- or γ-tocopherol.

Effect of sesaminol on plasma and tissue α-tocopherol and α-tocotrienol concentrations in rats fed a vitamin E concentrate rich in tocotrienols

We have shown that sesame lignans added to rat diet resulted in significantly greater plasma and tissue concentrations of α- and γ-tocopherol concentrations in supplemented rats than in rats without supplementation. In the present studies we examined whether sesaminol, a sesame lignan, enhances tocotrienol concentrations in plasma and tissues of rats fed diets containing a tocotrienol-rich fraction of palm oil (T-mix). In Ex-periment 1, effects of sesaminol on tocotrienol concentrations in plasma, liver, and kidney were evaluated in rats fed diets containing 20 mg/kg of T-mix (20T) and 50 mg/kg of T-mix (50T) with or without 0.1% sesaminol. Although the T-mix contained 23% α-tocopherol, 22% α-tocotrienol, and 34% γ-tocotrienol, α-tocopherol constituted most or all of the vitamin E in plasma and tissue (from 97% in kidney to 100% in plasma), with no or very little α-tocotrienol and no γ-tocotrienol at all. Addition of sesaminol to the T-mix resulted in significantly higher plasma, liver, and kidney α-tocopherol concentrations compared to values for T-mix alone. Further, T-mix with sesaminol resulted in significantly higher α-tocotrienol concentrations in kidney, although the concentration was very low. In Experiment 2, we examined whether sesaminol caused enhanced absorption of α-tocopherol and α-tocotrienol in a dosage regimen supplying T-mix and sesaminol on alternating days and observed significantly higher levels of α-tocopherol and α-tocotrienol in rats fed sesaminol, even without simultaneous intake, compared to those in rats without sesaminol. In Experiment 3, α-tocopherol was supplied to the stomach with and without sesaminol, and α-tocopherol concentrations in the lymph fluid were measured, α-Tocopherol concentrations were not different between groups. These results indicated that sesaminol produced markedly higher α-tocopherol concentrations in plasma and tissue and significantly greater α-tocotrienol concentrations in kidney and various other tissues, but the concentrations of α-tocotrienol were extremely low compared to those of α-tocopherol (Exps. 1 and 2). However, the sesaminol-induced increases of α-tocopherol and α-tocotrienol concentrations in plasma and tissue were not caused by their enhanced absorption since sesaminol did not enhance their absorption.