大麦籽粒生育酚和生育三烯酚的合成与分布特性

大麦生育酚(tocopherols,T)和生育三烯酚(tocotrienols,T3)是重要的抗氧化功效成分,对人体健康具有潜在的应用价值。本研究分析了大麦籽粒发育过程中生育酚和生育三烯酚及其异构体成分的含量和分布特性。结果表明:在大麦籽粒发育过程中,籽粒总生育酚和总生育三烯酚含量随籽粒发育进程不断升高,抽穗后发育第30~35天合成积累速率最快,占总含量50%左右;颖壳中的生育酚和生育三烯酚及其异构体含量显著低于去颖壳后籽粒中的含量;在籽粒发育不同阶段异构体α-T和α-T3含量较高且变化大,其他6种异构体(β-T、γ-T、δ-T、β-T3、γ-T3和δ-T3)含量低且基本恒定。说明大麦籽粒生育酚和生育三烯酚及其异构体成分的积累速率和分布存在显著差异。     

植物维生素E合成相关酶基因的克隆及其在体内功能研究进展

维生素E（VE）的天然产物有8种类型,分别为α、β、γ、δ-生育酚（tocopherol）和α、β、γ、δ-生育三烯酚（tocotrienol）,对植物、动物和人类都具有十分重要的生理作用。医学证明,维生素E不仅与生殖系统,而且与中枢神经系统、消化系统、心血管系统和肌肉系统的正常代谢都有密切关系;它也是治疗冠心病、动脉粥样硬化、贫血、脑软化、肝病和癌症等的辅助药物。而绿色植物则是人类和动物VE的基本来源。近年来随着植物基因组学的发展和营养基因组学概念的提出,通过快速分离植物营养代谢（VE）相关酶的基因,最终解析和调控植物微量营养素代谢途径,利用代谢工程的方法大大提高植物营养价值之策略正在逐步完善。本文对有关植物中VE生物合成途径和相关酶基因克隆研究现状,以及VE在植物体内的作用和功能研究进展进行了综述,以期为VE作用机理的探寻和功能开发提供新思路。     

天然生育酚的结构、生物合成和功能

生育酚是一类重要的脂溶性抗氧化荆,天然生育酚有α-、β-、γ-、δ—4种异构体,主要是以尿黑酸为前体在高等植物的叶绿体内膜上合成的。生育酚的主要功能是抗氧化作用,被广泛地应用于制药和食品工业中,开发和提取天然生育酚已引起关注与重视。     

植物维生素E基因工程研究进展

维生素E(vitamin E, VE)是一类由光合生物合成的、人类饮食中必不可少的两种抗氧化物质,分为生育酚和生育三烯酚两大类。除了生育酚类物质所具有的抗氧化作用外,生育三烯酚还有很强的降胆固醇、预防糖尿病、促进骨吸收、抗癌和神经保护的作用,因此,VE被广泛应用于医药、食品、化妆品等行业中。本文主要综述了植物维生素E生物合成相关酶的研究进展以及利用基因工程手段提高植物维生素E活性的新策略。其中,多基因共转化、多基因操纵子及质体转化等方法为提高植物维生素E活性提供了新的思路。     

维生素E对人体作用简介

维生素Ｅ是聚异戊二烯取代的６－羟基苯骈二氢吡喃衍生物,在苯环上有一个酚羟基。早年认为它有抗不育作用,故又名生育酚,自然界中具有维生素Ｅ活性的物质已知有８种,根据甲基的数目和位置不同,分为α、β、γ、δ、ζ、η等生育酚,以前４种较重要,α－生育酚生理活...     

拟南芥γ-生育酚甲基转移酶(γ-TMT)启动子的分离及表达特性分析

维生素E是一类人体所必需的脂溶性的维生素,具有重要的生理功能。γ-生育酚甲基转移酶(γ-TMT)是维生素E生物合成途径中的关键酶之一,催化γ、δ-生育酚甲基化,生成α、β-生育酚。从拟南芥中分离了γ-生育酚甲基转移酶基因1552bp的启动子序列,构建了含有该启动子和GUS报告基因的植物表达载体,通过农杆菌介导转化拟南芥,获得了转基因植株。GUS组织化学染色结果表明,在γ-TMT启动子的驱动下,报告基因GUS在拟南芥的叶、茎以及花均有表达,且在茎尖、雄蕊和幼叶中表达最强,而在根、种子和种荚中则没有检测到GUS基因的表达,表明γ-TMT基因可能仅在拟南芥某些组织中特异性高表达。     

HPLC法分析油菜种子油中维生素E的组成与含量

利用HPLC法分析了50份遗传背景丰富的白菜型油菜、甘蓝型油菜、芥菜型油菜和芸芥种子油中维生素E的组成与含量.研究结果显示,油菜种子油中主要含α-生育酚和γ -生育酚,且a-生育酚、γ-生育酚和维生素E总量均存在明显的基因型差异,甘蓝型油菜种子油中维生素E含量总体水平最高,平均总量较高,为123.11 mg/100g油,维生素E含量最高的Omega,总量为144.73 mg/100g油,α/γ-生育酚比值最高可达0.77.α-生育酚、γ-生育酚和维生素E总量与类胡萝卜素含量均呈现显著负相关,种子油中α-生育酚与含油量呈现显著正相关,α-生育酚、γ -生育酚和维生素E总量与生育期均呈现显著或极显著正相关,α-生育酚和维生素E总量与株高均呈现显著正相关,维生素E总量与千粒重呈显著正相关,而α-生育酚、γ-生育酚和维生素E总量与全株角果数和每角粒数相关不显著.     

利用微藻生产维生素E的研究现状与应用前景

维生素E（生育酚）是一种人体和动物所必需的脂溶性营养成分。植物油等组织是天然维生素E的重要来源之一。但植物组织中生育酚含量低,且大多为低活性类型。利用微藻进行维生素E生产很具商业化前景。其中裸藻生长速度快,α-生育酚含量高,可占生育酚总量的97％以上。对利用微藻生产维生素E的研究现状和应用进行了综述。     

三烯生育酚研究进展

三烯生育酚和生育酚统称为维生素E,是重要的脂溶性维生素。维生素E只能在植物或者光合细菌中合成,是人类和动物必需且只能通过食物等摄取的重要维生素。一直以来,由于三烯生育酚与生育酚相比,生物活性较低且分布范围较小,人们对其研究相对较少。近些年的研究发现,由于三烯生育酚和生育酚的结构相似,因此三烯生育酚具有与生育酚相同的抗氧化等功能;但又由于三烯生育酚含有不饱和的植基侧链,使得三烯生育酚还具有一些不同于生育酚的功能,比如保护神经免受损伤、降低胆固醇、保护脑细胞免受损伤等。因此,三烯生育酚逐渐成为了研究热点。根据维生素E的生物合成途径,人们也开始了对三烯生育酚的生物强化研究,其合成途径中第一个关键酶基因HGGT的过表达是目前三烯生育酚含量提高的最有效途径;将来还需结合其合成调控的分子机制及其吸收利用问题,开发针对三烯生育酚的功能型产品。从三烯生育酚的合成途径、生物学功能、生物强化等方面进行了综述,并对今后的研究重点提出了展望。     

维生素E的功能、吸收与代谢(1)

维生素E（VE）是生育酚（tocopherols）和生育三烯酚（tocotrienols）的总称,是人和动物生殖、生长过程中的必需微量营养物质,具有抗氧化、抗衰老、抗癌和抗热应激反应的作用,能增强动物体的免疫力,改善肌肉品质,还与某些基因相互作用影响转录和表达等。α-生育酚主要是在十二指肠通过淋巴吸收的,而且约99％是以乳糜微粒的形式吸收的。VE的代谢是其侧链在细胞色素P-450的启动下．先经ω-羟基化再β-氧化降解生成CEHC。CYP3A是ω-氧化酶,CYP3A催化的VEω-氧化是VE代谢的限速步骤。现代的研究拟从分子水平来理解和描述VE的代谢和作用机制。     

Tocotrienols confer resistance to ischemia in hypercholesterolemic hearts: insight with genomics

Most clinical trials with vitamin E could not lower cholesterol and thus, have been deemed unsuccessful. Recently, tocotrienols, isomers of vitamin E have been found to lower LDL levels. To explore if tocotrienols could be the drug target for vitamin E, rabbits were kept on cholesterol diet for 60 days supplemented with tocotrienol-α, tocotrienol-δ, and tocotrienol-γ for the last 30 days. The serum cholesterol levels (in mmol/l) were 24.4 (tocotrienol-α), 34.9 (tocotrienol-δ), 19.8 (tocotrienol-γ) vs. 39.7 (control). Left ventricular function including aortic flow and developed pressure exhibited significantly improved recovery with tocotrienol-γ and -α, but not with tocotrienol-δ. The myocardial infarct size showed a similar pattern: 33% (tocotrienol-α), 23% (tocotrienol-γ), and 47% (tocotrienol-δ). To examine the molecular mechanisms of cardioprotective effects, gene expression profile was determined using Atlas 1.2/1.2II followed by determination of gene profiles using PedQuest 8.3 software. Based on genomic profiles, the following cholesterol-related proteins were examined: FABP, TGF-β (cholesterol suppresses TGF-β), ET-1 (increased by hypercholesterolemia), SPOT 14 (linked with hypercholesterolemia), and matrix metalloproteinase (MMP) 2 and MMP9 (cholesterol regulates MMP2 and MMP9 expression) in the heart. Consistent with the cardioprotective effects of tocotrienol-α and -γ, these two isomers reduced ET-1, decreased MMP2 and MM9, increased TGF-β and reduced SPOT 14, while tocotrienol-δ had no effects. The results of the present study demonstrate that the two isomers of tocotrienols, α and γ, render the hypercholesterolemic hearts resistant to ischemic reperfusion injury by lowering several hypercholesterolemic proteins including MMP2, MMP9, ET-1, and SPOT 14 and upregulating TGF-β.     

A review of characterization of tocotrienols from plant oils and foods

Tocotrienols, members of the vitamin E family, are natural compounds found in a number of vegetable oils, wheat germ, barley and certain types of nuts and grains. Vegetable oils provide the best sources of these vitamin E forms, particularly palm oil and rice bran oil contain higher amounts of tocotrienols. Other sources of tocotrienols include grape fruit seed oil, oats, hazelnuts, maize, olive oil, buckthorn berry, rye, flax seed oil, poppy seed oil and sunflower oil. Tocotrienols are of four types, viz. alpha (α), beta (β), gamma (γ) and delta (δ). Unlike tocopherols, tocotrienols are unsaturated and possess an isoprenoid side chain. A number of researchers have developed methods for the extraction, analysis, identification and quantification of different types of vitamin E compounds. This article constitutes an in-depth review of the chemistry and extraction of the unsaturated vitamin E derivatives, tocotrienols, from various sources using different methods. This review article lists the different techniques that are used in the characterization and purification of tocotrienols such as soxhlet and solid–liquid extractions, saponification method, chromatography (thin layer, column chromatography, gas chromatography, supercritical fluid, high performance), capillary electrochromatography and mass spectrometry. Some of the methods described were able to identify one form or type while others could analyse all the analogues of tocotrienol molecules. Hence, this article will be helpful in understanding the various methods used in the characterization of this lesser known vitamin E variant.     

Tocotrienols: Balancing the Mitochondrial Crosstalk Between Apoptosis and Autophagy

Tocotrienols are a group of natural vitamin E compounds with patent antitumoral effects, mostly based on their ability to induce apoptosis in cancer cells. In activated pancreatic stellate cells (PSCs) we have determined that tocotrienols elicit a dramatic mitochondrial destabilization followed by initiation of non-necrotic forms of programmed cell death, namely apoptosis and autophagy. PSCs are the main cell type involved in the generation of pancreatic fibrosis, and their removal is critical to limit the fibrogenic process. Noteworthy, tocotrienol death-promoting actions are exclusively directed to activated PSCs, but not to their quiescent counterparts nor to terminally differentiated acinar cells. Here, we hypothesize that the transformed phenotype of PSCs may include “activated” mitochondria, which can be used by tocotrienols to trigger autophagic and apoptotic signaling. We propose that mitochondria are the cornerstone of cell sensitivity to tocotrienols, and suggest possible mechanisms, that may be interconnected, on how tocotrienols may govern mitochondrial death pathways.

Addendum to:

Tocotrienols Induce Apoptosis and Autophagy in Rat Pancreatic Stellate Cells through the Mitochondrial Death Pathway

M. Rickmann, E.C. Vaquero, J.R. Malagelada and X. Molero

Gastroenterology 2007; 132:2518-32     

Tocotrienols promote apoptosis in human breast cancer cells by inducing poly(ADP‐ribose) polymerase cleavage and inhibiting nuclear factor kappa‐B activity

Objectives

Tocotrienols and tocopherols are members of the vitamin E family, with similar structures; however, only tocotrienols have been reported to achieve potent anti‐cancer effects. The study described here has evaluated anti‐cancer activity of vitamin E to elucidate mechanisms of cell death, using human breast cancer cells.

Materials and methods

Anti‐cancer activity of a tocotrienol‐rich fraction (TRF) and a tocotrienol‐enriched fraction (TEF) isolated from palm oil, as well as pure vitamin E analogues (α‐tocopherol, α?, δ? and γ?tocotrienols) were studied using highly aggressive triple negative MDA‐MB‐231 cells and oestrogen‐dependent MCF‐7 cells, both of human breast cancer cell lines. Cell population growth was evaluated using a Coulter particle counter. Cell death mechanism, poly(ADP‐ribose) polymerase cleavage and levels of NF‐κB were determined using commercial ELISA kits.

Results

Tocotrienols exerted potent anti‐proliferative effects on both types of cell by inducing apoptosis, the underlying mechanism of cell death being ascertained using respective IC₅₀ concentrations of all test compounds. There was marked induction of apoptosis in both cell lines by tocotrienols compared to treatment with Paclitaxel, which was used as positive control. This activity was found to be associated with cleavage of poly(ADP‐ribose) polymerase (a DNA repair protein), demonstrating involvement of the apoptotic cell death signalling pathway. Tocotrienols also inhibited expression of nuclear factor kappa‐B (NF‐κB), which in turn can increase sensitivity of cancer cells to apoptosis.

Conclusion

Tocotrienols induced anti‐proliferative and apoptotic effects in association with DNA fragmentation, poly(ADP‐ribose) polymerase cleavage and NF‐κB inhibition in the two human breast cancer cell lines.

     

Natural forms of vitamin E: metabolism,antioxidant, and anti-inflammatory activities and their role in disease prevention and therapy

The vitamin E family consists of four tocopherols and four tocotrienols. α-Tocopherol (αT) is the predominant form of vitamin E in tissues and its deficiency leads to ataxia in humans. However, results from many clinical studies do not support a protective role of αT in disease prevention in people with adequate nutrient status. On the other hand, recent mechanistic studies indicate that other forms of vitamin E, such as γ-tocopherol (γT), δ-tocopherol, and γ-tocotrienol, have unique antioxidant and anti-inflammatory properties that are superior to those of αT in prevention and therapy against chronic diseases. These vitamin E forms scavenge reactive nitrogen species, inhibit cyclooxygenase- and 5-lipoxygenase-catalyzed eicosanoids, and suppress proinflammatory signaling such as NF-κB and STAT3/6. Unlike αT, other vitamin E forms are significantly metabolized to carboxychromanols via cytochrome P450-initiated side-chain ω-oxidation. Long-chain carboxychromanols, especially 13′-carboxychromanols, are shown to have stronger anti-inflammatory effects than unmetabolized vitamins and may therefore contribute to the beneficial effects of vitamin E forms in vivo. Consistent with mechanistic findings, animal and human studies show that γT and tocotrienols may be useful against inflammation-associated diseases. This review focuses on non-αT forms of vitamin E with respect to their metabolism, anti-inflammatory effects and mechanisms, and in vivo efficacy in preclinical models as well as human clinical intervention studies.     

Selective excretion of yolk-derived tocotrienols into the bile of the chick embryo

The aim of this study was to investigate the possibility of biodiscrimination between different forms of vitamin E during the development of the chick embryo. The vitamin E present in the initial yolk consisted of α-tocopherol (90%), (β+γ)-tocopherol (8%), α-tocotrienol (0.3%) and (β+γ)-tocotrienol (1.3%). In marked contrast, the vitamin E recovered from the bile of the day-16 embryo contained much higher proportions of α-tocotrienol (10%) and especially of (β+γ)-tocotrienol (42%). By the time of hatching, 56% of the vitamin E present in the bile was in the form of (β+γ)-tocotrienol. The residual yolk of the newly-hatched chick contained far greater proportions of α-tocotrienol (2.6%) and (β+γ)-tocotrienol (10%) than were present in the initial yolk. The results suggest that the liver of the embryo may selectively excrete tocotrienols as components of bile, whilst retaining the tocopherols within the hepatocytes. The increased proportions of tocotrienols in the residual yolk may result from the recycling of bile from the gall bladder to the yolk. The liver of the day-old chick contained α-tocopherol as the main form of vitamin E (90%) with only a small proportion (0.2%) of (β+γ)-tocotrienol. The α-tocopherol form was also the main vitamin E component in the brain (85%), heart (79%), lung (82%) and adipose tissue (91%) of the day-old chick. The present study suggests the occurrence of a high degree of biodiscrimination between tocopherols and tocotrienols during the development of the chick embryo.     

Unleashing the untold and misunderstood observations on vitamin E

Paradoxically, meta-analysis of human randomized controlled trials revealed that natural but not synthetic α-tocopherol supplementation significantly increases all-cause mortality at 95% confidence interval. The root cause was that natural α-tocopherol supplementation significantly depressed bioavailability of other forms of vitamin E that have better chemo-prevention capability. Meta-analysis outcome demonstrated flaws in the understanding of vitamin E. Reinterpretation of reported data provides plausible explanations to several important observations. While α-tocopherol is almost exclusively secreted in chylomicrons, enterocytes secrete tocotrienols in both chylomicrons and small high-density lipoproteins. Vitamin E secreted in chylomicrons is discriminately repacked by α-tocopherol transfer protein into nascent very low-density lipoproteins in the liver. Circulating very low-density lipoproteins undergo delipidation to form intermediate-density lipoproteins and low-density lipoproteins. Uptake of vitamin E in intermediate-density lipoproteins and low-density lipoproteins takes place at various tissues via low-density lipoproteins receptor-mediated endocytosis. Small high-density lipoproteins can deliver tocotrienols upon maturation to peripheral tissues independent of α-tocopherol transfer protein action, and uptake of vitamin E takes place at selective tissues by scavenger receptor-mediated direct vitamin E uptake. Dual absorption pathways for tocotrienols are consistent with human and animal studies. α-Tocopherol depresses the bioavailability of α-tocotrienol and has antagonistic effect on tocotrienols in chemo-prevention against degenerative diseases. Therefore, it is an undesirable component for chemo-prevention. Future research directions should be focused on tocotrienols, preferably free from α-tocopherol, for optimum chemo-prevention and benefits to mankind.     

Metabolic redesign of vitamin E biosynthesis in plants for tocotrienol production and increased antioxidant content

Tocotrienols are the primary form of vitamin E in seeds of most monocot plants, including cereals such as rice and wheat. As potent antioxidants, tocotrienols contribute to the nutritive value of cereal grains in human and livestock diets. cDNAs encoding homogentisic acid geranylgeranyl transferase (HGGT), which catalyzes the committed step of tocotrienol biosynthesis, were isolated from barley, wheat and rice seeds. Transgenic expression of the barley HGGT in Arabidopsis thaliana leaves resulted in accumulation of tocotrienols, which were absent from leaves of nontransformed plants, and a 10- to 15-fold increase in total vitamin E antioxidants (tocotrienols plus tocopherols). Overexpression of the barley HGGT in corn seeds resulted in an increase in tocotrienol and tocopherol content of as much as six-fold. These results provide insight into the genetic basis for tocotrienol biosynthesis in plants and demonstrate the ability to enhance the antioxidant content of crops by introduction of an enzyme that redirects metabolic flux.     

Tocotrienols in Vellozia gigantea leaves: occurrence and modulation by seasonal and plant size effects

Vitamin E occurs in all photosynthetic organisms examined to date. Tocopherols predominate in photosynthetic tissues (α-tocopherol being the major form), while either tocopherols or tocotrienols (or both) are present in seeds. Tocotrienols have not been described in photosynthetic tissues thus far. Here, we report on the presence of tocotrienols in leaves of higher plants. Both tocopherols and tocotrienols accumulated in leaves of Vellozia gigantea, an endemic plant found in the rupestrian fields of Serra do Cipó, Brazil. Increased plant size had a remarkable effect on the vitamin E composition of leaves, α-tocopherol and β-tocotrienol levels being highest in the largest individuals, but only during the dry season. Vitamin E levels positively correlated with lipid hydroxyperoxide levels, which also increased in the largest individuals during the dry season. However, the maximum efficiency of PSII photochemistry (F _v/F _m ratio) kept above 0.75 throughout the experiment, thus indicating absence of photoinhibitory damage to the photosynthetic apparatus. It is concluded that higher plants, such as V. gigantea, can accumulate tocotrienols in leaves, aside from tocopherols, and that the levels of both tocopherols and tocotrienols in the leaves of this species are strongly modulated by seasonal and plant size effects.