Do tocotrienols have potential as neuroprotective dietary factors?

α-Tocopherol transfer protein is not required for the discrimination against γ-tocopherol in vivo but protects it from side-chain degradation in vitro

SCOPE

The mechanisms underlying the preferential retention of a single compound (α-tocopherol (αT)) of the eight vitamin E compounds in the body are incompletely understood. We hypothesized that vitamin E metabolism and not the hepatic α-tocopherol transfer protein (TTP) is responsible for the discrimination against non-αT congeners.

METHODS AND RESULTS

TTP knockout and wild-type mice (n = 12/group) were fed equimolar concentrations of αT and γ-tocopherol (γT; 50 mg/kg diet each) alone or together with sesamin (2 g/kg diet) for 6 wk. Inhibition of vitamin E metabolism with sesamin, but not TTP knockout, increased γT tissue concentrations. TTP-expressing and TTP-free cells were incubated with equimolar concentrations of αT and γT (25 μmol/L each) with or without sesamin (2 μmol/L). The preferential degradation of γT independently of TTP expression was confirmed and a decrease in the production of the metabolite γ-carboxyethyl hydroxychromanol (CEHC) with increasing TTP expression revealed. Displacing γT from TTP in these cells by incubation with increasing αT concentrations enhanced the secretion of γ-CEHC in TTP-transfected cells, suggesting that TTP might protect γT from β-oxidation.

CONCLUSIONS

We conclude that vitamin E metabolism and not TTP controls γT concentrations in vivo and observed an interaction of TTP with vitamin E metabolism that results in reduced production of the metabolite γ-CEHC.

Vitamin E tocotrienol supplementation improves lipid profiles in chronic hemodialysis patients

PURPOSE

Chronic hemodialysis patients experience accelerated atherosclerosis contributed to by dyslipidemia, inflammation, and an impaired antioxidant system. Vitamin E tocotrienols possess anti-inflammatory and antioxidant properties. However, the impact of dietary intervention with Vitamin E tocotrienols is unknown in this population.

PATIENTS AND METHODS

A randomized, double-blind, placebo-controlled, parallel trial was conducted in 81 patients undergoing chronic hemodialysis. Subjects were provided daily with capsules containing either vitamin E tocotrienol-rich fraction (TRF) (180 mg tocotrienols, 40 mg tocopherols) or placebo (0.48 mg tocotrienols, 0.88 mg tocopherols). Endpoints included measurements of inflammatory markers (C-reactive protein and interleukin 6), oxidative status (total antioxidant power and malondialdehyde), lipid profiles (plasma total cholesterol, triacylglycerols, and high-density lipoprotein cholesterol), as well as cholesteryl-ester transfer protein activity and apolipoprotein A1.

RESULTS

TRF supplementation did not impact any nutritional, inflammatory, or oxidative status biomarkers over time when compared with the baseline within the group (one-way repeated measures analysis of variance) or when compared with the placebo group at a particular time point (independent t-test). However, the TRF supplemented group showed improvement in lipid profiles after 12 and 16 weeks of intervention when compared with placebo at the respective time points. Normalized plasma triacylglycerols (cf baseline) in the TRF group were reduced by 33 mg/dL (P=0.032) and 36 mg/dL (P=0.072) after 12 and 16 weeks of intervention but no significant improvement was seen in the placebo group. Similarly, normalized plasma high-density lipoprotein cholesterol was higher (P<0.05) in the TRF group as compared with placebo at both week 12 and week 16. The changes in the TRF group at week 12 and week 16 were associated with higher plasma apolipoprotein A1 concentration (P<0.02) and lower cholesteryl-ester transfer protein activity (P<0.001).

CONCLUSION

TRF supplementation improved lipid profiles in this study of maintenance hemodialysis patients. A multi-centered trial is warranted to confirm these observations.

Rice bran extract protects from mitochondrial dysfunction in guinea pig brains

Mitochondrial dysfunction plays a major role in the development of age-related neurodegenerative diseases and recent evidence suggests that food ingredients can improve mitochondrial function. In the current study we investigated the effects of feeding a stabilized rice bran extract (RBE) on mitochondrial function in the brain of guinea pigs. Key components of the rice bran are oryzanols, tocopherols and tocotrienols, which are supposed to have beneficial effects on mitochondrial function. Concentrations of α-tocotrienol and γ-carboxyethyl hydroxychroman (CEHC) but not γ-tocotrienol were significantly elevated in brains of RBE fed animals and thus may have provided protective properties. Overall respiration and mitochondrial coupling were significantly enhanced in isolated mitochondria, which suggests improved mitochondrial function in brains of RBE fed animals. Cells isolated from brains of RBE fed animals showed significantly higher mitochondrial membrane potential and ATP levels after sodium nitroprusside (SNP) challenge indicating resistance against mitochondrial dysfunction. Experimental evidence indicated increased mitochondrial mass in guinea pig brains, e.g. enhanced citrate synthase activity, increased cardiolipin as well as respiratory chain complex I and II and TIMM levels. In addition levels of Drp1 and fis1 were also increased in brains of guinea pigs fed RBE, indicating enhanced fission events. Thus, RBE represents a potential nutraceutical for the prevention of mitochondrial dysfunction and oxidative stress in brain aging and neurodegenerative diseases.

Rapid baseline-separation of all eight tocopherols and tocotrienols by reversed-phase liquid-chromatography with a solid-core pentafluorophenyl column and their sensitive quantification in plasma and liver

Of the eight natural vitamin E congeners (α-, β-, γ-, and δ-tocopherol and α-, β-, γ-, and δ-tocotrienol), the non-α-tocopherol congeners have unique biological properties that may contribute to human health. Their study in vivo has been complicated by the lack of a simple analytical method that completely resolves and sensitively detects all eight natural tocopherols and tocotrienols in biological matrices. We thus developed and validated (according to the FDA guidelines for bioanalytical method validation) the first reversed-phase liquid chromatographic method for the baseline-separation and quantification of all eight tocopherols and tocotrienols. Analytes were extracted from human plasma or mouse liver and separated on a Phenomenex Kinetex PFP column (2.6 μm, 150 × 4.6 mm) by elution with methanol:water (85:15, vol/vol) at a flow rate of 0.8 mL/min. The developed RP-LC method used a solid-core pentafluorophenyl stationary phase and achieved baseline separation of all eight vitamin E congeners within 15 min at a backpressure of 23 MPa, which is suitable for most conventional HPLC systems. The method was fast, linear, accurate, and precise with detection limits of 27-156 pg and good recoveries (82-122%) for all analytes. In conclusion, we developed and validated the first RP-LC method for baseline resolution of all eight tocopherols and tocotrienols extracted from plasma and liver, which should be useful for the quantification of individual vitamin E congeners in large epidemiological studies and randomized controlled trials.

Tocotrienols prevent hydrogen peroxide-induced axon and dendrite degeneration in cerebellar granule cells

It is well known that reactive oxygen species (ROS) attack several living tissues and increase the risk of development and progression of serious diseases. In neuronal level, ROS induce cell death in concentration-dependent fashion. However, little is known about the mechanisms of neuronal changes by ROS prior to induction of cell death. Here we found that treatment of cerebellar granule neurons (CGCs) with 0.5 μM hydrogen peroxide induced axonal injury, but not cell death. The number of dendrites remarkably decreased in hydrogen peroxide-treated CGCs, and extensive beading was observed on survival dendrites. In addition, an abnormal band of the original collapsin response mediator protein (CRMP)-2 was detected by Western blotting in hydrogen peroxide-treated CGCs. Treatment with each tocotrienol isoform prevented axonal and dendrite degeneration and induction of the abnormal band of the original band of CRMP-2 in hydrogen peroxide-treated CGCs. These results indicate that treatment with tocotrienols may therefore be neuroprotective in the presence of hydrogen peroxide by preventing changes to the CRMP-2 that occur before neuron death.