Identification of a Genetic Factor Required for High γ‑Isoform Concentration in Rice Vitamin E

The γ-isoforms of tocopherols (Tc) and tocotrienols (T3) possess high biological activities in comparison to the α-isoforms. The concentrations of Tc and T3 isoforms in rice (Oriza sativa) was cultivar-dependent. Using chromosome segment substitution lines (CSSLs) and near isogenic lines (NILs) of indica cultivar “Kasalath” in a japonica cultivar “Koshihikari” genetic background, the Kasalath genomic segment on chromosome 2 was determined to be responsible for the high γ-isoform concentration: γ-tocopherol methyltransferase (<i>γ-TMT</i>) was identified as a candidate gene. An amino acid substitution in the coding region and several nucleotide polymorphisms, including an insertion of 10 base pairs in the promoter region, were identified. Gene expression analysis revealed that low expression levels of the <i>γ-TMT</i> gene in Kasalath were not associated with the γ-isoform concentration. Genetic variations in the coding region of the <i>γ-TMT</i> gene may play a major role in determining the γ-isoform concentration. This information could be used to breed rice with a high γ-isoform content

α‑Tocopherol Attenuates the Triglyceride- and Cholesterol-Lowering Effects of Rice Bran Tocotrienol in Rats Fed a Western Diet

Previous studies demonstrated the ability of tocotrienol (T3) to lower levels of lipids, including cholesterol (Cho) and triglycerides (TG). Although α-tocopherol (α-Toc) reportedly inhibits the hypocholesterolemic effect of T3, there is no information about whether α-Toc influences the TG-lowering effect of T3 in vivo. In this study, we investigated the influence of α-Toc on the antihyperlipidemic effects (Cho- and TG-lowering) of rice bran tocotrienols (RBT3) in F344 rats fed a western diet. α-Toc attenuated both the Cho- and TG-lowering effects of RBT3 in vivo, whereas α-Toc alone exhibited no hypolipidemic effects. RBT3-induced <i>Cpt-1a</i> and <i>Cyp7a1</i> gene expression was reduced by α-Toc. Furthermore, coadministration of α-Toc decreased liver and adipose tissue concentrations of tocotrienols in F344 rats. These results indicate that α-Toc has almost no antihyperlipidemic effect in vivo, but abrogates the antihyperlipidemic effect of RBT3 by reducing tissue concentrations of tocotrienols and regulating expression of genes involved in lipid metabolism. Understanding the underlying mechanism of the beneficial effects of T3 on lipid metabolism and the interaction with α-Toc will be important for developing T3-based therapeutics

The chromatograms of administration samples.

<p>Aza-sugars in each sample were analyzed using LC-MS/MS.</p

The transition of plasma DNJ concentration.

<p>The rats received orally administered sucrose (2 g/kg B.W.) 15 minutes after each samples administration (equivalent to 5 mg DNJ or miglitol/kg B.W.). Blood was collected from tail venous vein and plasma DNJ or miglitol concentration was determined using LC-MS/MS. Results are given as means ± SE. Means without a common letter differ significantly (p < 0.05).</p

The recovery rate of ¹⁵N from DNJ in urine and feces until 48 hours after sample administration.

<p>The recovery rate of ¹⁵N from DNJ in urine and feces until 48 hours after sample administration. After 12 hours fasting, the rats were received ¹⁵N-labeled DNJ (10 mg). Urine and feces were collected and the amount of ¹⁵N from DNJ was analyzed. (a) The time course of recovery rate of ¹⁵N in urine. (b) Total recovery rate of ¹⁵N in urine and feces. Results are given as means ± SE.</p

The effects in suppressing the blood glucose in rats.

<p>The rats received orally administered sucrose (2 g/kg B.W.) 15 minutes after each samples administration (equivalent to 5 mg DNJ or miglitol/kg B.W.). Blood glucose levels were determined from tail blood sample. (a) is the transition of blood glucose concentration and (b) is area of under curve of blood glucose concentration. Results are given as means ± SE. * p < 0.05 versus control; ** p < 0.01 versus control.</p

The aza-sugars composition of administration samples.

<p>The aza-sugars composition of administration samples.</p