Tocotrienols, vitamin E compounds that have an unsaturated side chain with three double bonds, selectively inhibited the activity of mammalian DNA polymerase lambda (pol lambda) in vitro. These compounds did not influence the activities of replicative pols such as alpha, delta, and epsilon, or even the activity of pol beta which is thought to have a very similar three-dimensional structure to the pol beta-like region of pol lambda. Since delta-tocotrienol had the strongest inhibitory effect among the four (alpha- to delta-) tocotrienols, the isomer’s structure might be an important factor in the inhibition of pol lambda. The inhibitory effect of delta-tocotrienol on both intact pol lambda (residues 1-575) and a truncated pol lambda lacking the N-terminal BRCA1 C-terminus (BRCT) domain (residues 133-575, del-1 pol lambda) was dose-dependent, with 50% inhibition observed at a concentration of 18.4 and 90.1microM, respectively. However, del-2 pol lambda (residues 245-575) containing the C-terminal pol beta-like region was unaffected. Tocotrienols also inhibited the proliferation of and formation of tubes by bovine aortic endothelial cells, with delta-tocotrienol having the greatest effect. These results indicated that tocotrienols targeted both pol lambda and angiogenesis as anti-cancer agents. The relationship between the inhibition of pol lambda and anti-angiogenesis by delta-tocotrienol was discussed.
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Tocochromanols are a group of four tocopherols and four tocotrienols that collectively constitute vitamin E, an essential nutrient in the human diet. Tocochromanols are only synthesized in oxygenic photosynthetic organisms. Although they have similar antioxidant activities in vitro, the individual tocochromanols vary widely in their in vivo vitamin E activities. During the past several years, mutant and transgenic approaches in model organisms, particularly in Arabidopsis thaliana and Synechocystis sp. PCC6803, have allowed the full complement of core pathway genes to be isolated and studied. Pathway engineering with these genes has provided significant insights into the molecular genetic and biochemical control of tocochromanol biosynthesis in plants. The resulting knowledge base is driving efforts to manipulate the levels of this essential nutrient in staple crops for populations in the developed and developing world.
A normal-phase high-performance liquid chromatography (NP-HPLC) method for the determination of tocopherols and tocotrienols in hazelnuts is reported. Three extraction procedures (with and without saponification) were assayed; the best results were obtained with a simple solid-liquid extraction procedure. Chromatographic separation was achieved using an Inertsil 5 SI column using isocratic elution with hexane/1,4-dioxane (95.5:4.5, v/v) at a flow rate of 0.7 mL/min. The effluent was monitored by a series arrangement of a diode-array followed by a fluorescence detector. All compounds were separated in a short period of time (17 min). The method proved to be rapid, sensitive, reproducible and accurate, allowing the simultaneous determination of all vitamin E homologues.
Purpose: To evaluate the potential of the vitamin E compound alpha-tocotrienol as antifibrotic agent in vitro.
Methods: Using human Tenon’s capsule fibroblast cultures, the antiproliferative and cytotoxic effects of the different vitamin E forms alpha-tocopherol, alpha-tocopheryl acetate, alpha-tocopheryl succinate and alpha-tocotrienol were compared with those of mitomycin C. To mimic subconjunctival and regular oral application in vivo, exposure time of serum-stimulated and serum-restimulated fibroblasts (SF and RF, respectively) to vitamin E forms was set at 6 days. Cultures were only exposed for 5 min to mitomycin C due to its known acute toxicity and to mimic the short-time intraoperative administration. Proliferation (expressed as % of control) was determined by DNA content quantification on days 2, 4 and 6, whereas cytotoxicity was assessed by cell morphology and glucose 6-phosphate dehydrogenase (G6PD) release after 24 h.
Results: alpha-Tocopherol and alpha-tocopheryl acetate stimulated growth of SF, but not RF. Reduction of fibroblast content by alpha-tocopheryl succinate was accompanied by increased G6PD release and necrosis. Contrary to alpha-tocopheryl succinate, 50 microM or repeatedly 20 microM of alpha-tocotrienol significantly inhibited proliferation without causing cellular toxicity (maximal effect: 46.8%). RF were more sensitive to this effect than SF. Mitomycin C 100-400 microg/ml showed a stronger antiproliferative effect than alpha-tocotrienol (maximal effect: 13.8%). Morphologic characteristics of apoptosis were more commonly found under treatment with mitomycin C.
Conclusions: Of the vitamin E forms tested, only alpha-tocotrienol significantly inhibited growth at non-toxic concentrations. In this in vitro study, antiproliferative effects of mitomycin C were stronger than those of alpha-tocotrienol.
Activation of the NO-cGMP pathway is associated with myocardial protection against ischemia. During ischemia, function of this pathway is disturbed. Little is known about the effects of supplements such as Red Palm Oil (RPO) on the myocardial NO- cGMP- signalling pathway. RPO consists of saturated (SFAs), mono-unsaturated (MUFAs) and polyunsaturated (PUFAs) fatty acids and is an antioxidant rich in natural B-carotene and vitamin E (tocopherols and tocotrienols). This study determined whether dietary RPO-supplementation protects against the consequences of ischemia and identified a possible mechanism for this protection. Long-Evans rats were fed a control diet or control diet plus 7 g RPO per kg diet for six weeks. Hearts were excised and mounted on a working heart perfusion apparatus. Cardiac function was measured before and after hearts were subjected to 25 minutes of global ischemia. Left ventricular systolic (LVSP) and diastolic pressure (LVDP), coronary flow (CF), heart rate (HR) and aortic output (AO) were measured. To assess NO-cGMP pathway activity, hearts subjected to the same conditions, were freeze-clamped and analysed for tissue cAMP and cGMP levels using a RIA method. Furthermore, composition of myocardial phospholipid fatty acids by gas chromatography and blood samples were collected for serum lipid determinations. The percentage aortic output recovery of hearts supplemented with RPO was 72.9 +/-3.43% vs 55.4 +/-2.48% for controls (P< 0.05). Ten minutes into ischemia the cGMP levels of the RPO-supplementation group were significantly higher than the control group (26.5+/-2.78 pmol/g vs 10.1+/-1.78 pmol/g. Total myocardial PUFA content in hearts supplemented with RPO increased from 54.45+/-1.11% before ischemia to 59.03 +/- 0.30% after ischemia P<0.05). Results demonstrated that RPO-supplementation protected hearts against the consequences of ischemia/reperfusion injury. These findings suggest that dietary RPO protects via the NO-cGMP pathway and/or changes in PUFA composition during ischemia/reperfusion.
The natural vitamin E tocotrienol (TCT) possesses biological properties not shared by tocopherols (TCP). Nanomolar alpha-TCT, not alpha-TCP, is potently neuroprotective (JBC 275:13049; 278:43508). Tocopherol-transport protein (TTP) represents the primary mechanism for maintaining normal alpha-TCP concentrations in plasma and extrahepatic tissues. TTP primarily transports alpha-TCP and has low affinity for alpha-TCT. There are no studies that have investigated tissue delivery of alpha-TCT when orally gavaged on a long-term basis. A long-term study was conducted to examine the effects of alpha-TCT or alpha-TCP supplementation, either alone or in combination, on tissue levels. Rats were maintained on a vitamin E-deficient diet and gavaged with alpha-TCT or alpha-TCP alone or in combination. Five generations of rats were studied over 60 weeks. TTP-deficient mice were supplemented with TCT and bred to examine tissue delivery of oral alpha-TCT. Orally supplemented alpha-TCT was effectively delivered to most tissues over time. When co-supplemented, alpha-TCP outcompeted alpha-TCT for transport systems delivering vitamin E to tissues. To evaluate the significance of TTP in alpha-TCT delivery to tissues, tissue levels of alpha-TCT in supplemented TTP-deficient mice were studied. alpha-TCT was transported to several vital organs in TTP-deficient mice. alpha-TCT restored fertility in TTP-deficient mice. In sum, orally supplemented alpha-TCT was successfully delivered to several vital organs. The transport efficiency of alpha-TCT to tissues may be maximized by eliminating the co-presence of alpha-TCP in the oral supplement. Examination of whether alpha-TCT may benefit humans suffering from neurological disorders because of congenital TTP deficiency is warranted.
A high performance liquid chromatographic (HPLC) method for the determination of tocopherols and tocotrienols in walnut samples is described. The compounds were extracted with n-hexane, using a simple solid-liquid extraction procedure. Tocol was used as internal standard and BHT as anti-oxidant. The ehromatographic separation was achieved using an Inertsil 5 SI normal phase column operating with isocratic elution of n-hexane/1,4-dioxane (96.5:3.5, v/v), at a flow rate of 0.7 mL/min. The effluent was monitored by a series arrangement of a diodearray detector followed by a fluorescence detector. The detection limits were low, between 0.037 and 0.266 (jig/mL. The method was precise (% CV less than 2.8%), accurate (% CV less than 5.6%), and, as a general rule, the recovery values were high (mean values ranging from 93.4% to 104.0%)
The term vitamin E denotes a family of tocopherols and tocotrienols, plant lipids that are essential for vertebrate fertility and health. The principal form of vitamin E found in humans, RRR-alpha-tocopherol (TOH), is thought to protect cells by virtue of its ability to quench free radicals, and functions as the main lipid-soluble antioxidant. Regulation of vitamin E homeostasis occurs in the liver, where TOH is selectively retained while other forms of vitamin E are degraded. Through the action of tocopherol transfer protein (TTP), TOH is then secreted from the liver into circulating lipoproteins that deliver the vitamin to target tissues. Presently, very little is known regarding the intracellular transport of vitamin E. We utilized biochemical, pharmacological, and microscopic approaches to study this process in cultured hepatocytes. We observe that tocopherol-HDL complexes are efficiently internalized through scavenger receptor class B type I. Once internalized, tocopherol arrives within approximately 30 min at intracellular vesicular organelles, where it co-localizes with TTP, and with a marker of the lysosomal compartment (LAMP1), before being transported to the plasma membrane in a TTP-dependent manner. We further show that intracellular processing of tocopherol involves a functional interaction between TTP and an ABC-type transporter.
Tocochromanols (tocopherols and tocotrienols) are important lipophilic antioxidants for animals and humans. Their biological activity is expressed as vitamin E activity. This article describes the current need for vitamin E production, and compares different strategies to engineer the vitamin E content in photosynthetic bacteria and plants, with a focus on oilseed as target tissues. The current status of biotechnological advances in tocochromanol pathway engineering is summarized, and current limitations in our understanding of the tocochromanol biosynthetic pathway are discussed.
Free radicals generated by ferric nitrilotriacetate (FeNTA) can activate osteoclastic activity and this is associated with elevation of the bone resorbing cytokines interleukin (IL)-1 and IL-6. In the present study, we investigated the effects of 2 mg/kg FeNTA (2 mg iron/kg) on the levels of serum IL-1 and IL-6 with or without supplementation with a palm oil tocotrienol mixture or alpha-tocopherol acetate in Wistar rats. 2. The FeNTA was found to elevate levels of IL-1 and IL-6. Only the palm oil tocotrienol mixture at doses of 60 and 100 mg/kg was able to prevent FeNTA-induced increases in IL-1 (P < 0.01). Both the palm oil tocotrienol mixture and alpha-tocopherol acetate, at doses of 30, 60 and 100 mg/kg, were able to reduce FeNTA-induced increases in IL-6 (P < 0.05). Therefore, the palm oil tocotrienol mixture was better than pure alpha-tocopherol acetate in protecting bone against FeNTA (free radical)-induced elevation of bone-resorbing cytokines. 3. Supplementation with the palm oil tocotrienol mixture or alpha-tocopherol acetate at 100 mg/kg restored the reduction in serum osteocalcin levels due to ageing, as seen in the saline (control) group (P < 0.05). All doses of the palm oil tocotrienol mixture decreased urine deoxypyridinoline cross-link (DPD) significantly compared with the control group, whereas a trend for decreased urine DPD was only seen for doses of 60 mg/kg onwards of alpha-tocopherol acetate (P < 0.05). 4. Bone histomorphometric analyses have shown that FeNTA injections significantly lowered mean osteoblast number (P < 0.001) and the bone formation rate (P < 0.001), but raised osteoclast number (P < 0.05) and the ratio of eroded surface/bone surface (P < 0.001) compared with the saline (control) group. Supplementation with 100 mg/kg palm oil tocotrienol mixture was able to prevent all these FeNTA-induced changes, but a similar dose of alpha-tocopherol acetate was found to be effective only for mean osteoclast number. Injections of FeNTA were also shown to reduce trabecular bone volume (P < 0.001) and trabecular thickness (P < 0.05), whereas only supplementation with 100 mg/kg palm oil tocotrienol mixture was able to prevent these FeNTA-induced changes