Vitamin E: a vitamin still awaiting the detection of its biological function

Determining the rates of α-tocopherol movement in DPPC vesicles using small-angle neutron scattering

α-tocopherol (αtoc; vitamin E) is an essential nutrient sufficiently acquired through a balanced diet. This fat-soluble vitamin is most known for its antioxidative properties; however, its fundamental mechanism of action in cellular membranes remains unknown. To this end, we use time-resolved small-angle neutron scattering and a contrast matching scheme to determine the intervesicular exchange (kex) and intrabilayer flip-flop (kf) rates of αtoc in 1,2-dipalmitoyl-sn-glycero-3-phosphocholine vesicles. Moreover, we investigate the role of vesicle concentration and various types of cyclodextrins in affecting these rates. For a 25 mg/mL sample concentration, it was determined that kex and kf were 1.35 ± 0.03 × 10-3 and 0.54 ± 0.10 × 10-3 min-1, which represent half-lives of 513.4 ± 11.7 and 1285.1 ± 242.7 min, respectively. Differential scanning calorimetry confirmed the observed timescales of αtoc movement.

Modulation of the chain-breaking antioxidant activity of phenolic organochalcogens with various co-antioxidants at various pH values

Phenolic organochalcogen chain-breaking antioxidants, i.e. 6-bromo-8 (hexadecyltellanyl)-3,3-dimethyl-1,5-dihydro-[1,3]dioxepino[5,6-c]pyridin-9-ol and 2-methyl-2,3-dihydrobenzo[b]selenophene-5-ol, have been investigated in a two-phase (chlorobenzene/water) lipid peroxidation model system as potent inhibitors of lipid peroxyl radicals with various co-antioxidants at various pH values. The pH has a significant effect on the chain-breaking antioxidant activities of phenolic organochalcogens. The key chain-breaking mechanism profile was attributed to the first oxygen atom transfer from the lipid peroxyl radicals to the Se/Te atom, followed by hydrogen atom transfer in a solvent cage from the nearby phenolic group to the resulting alkoxyl radical. Finally, regeneration of organochalcogen antioxidants could take place in the presence of aqueous-soluble co-antioxidants. Also, in the presence of aqueous soluble N-acetylcysteine at pH 1-7, both antioxidants behaved as very good inhibitors of lipid peroxyl radicals. The role of aqueous soluble mild co-antioxidants in the regeneration studies of organochalcogen antioxidants has been investigated in a two-phase lipid peroxidation model system. The importance of the phase transfer catalyst has been explored in the inhibition studies of selenium containing antioxidants using an Fe(II) source. The overall pH-dependent antioxidant activities of organochalcogens depend on their hydrogen atom transfer ability, relative stability, and distribution in the aqueous/lipid phase.

Vitamin E Does Not Disturb Polyunsaturated Fatty Acid Lipid Domains

The function of vitamin E in biomembranes remains a prominent topic of discussion. As its limitations as an antioxidant persist and novel functions are discovered, our understanding of the role of vitamin E becomes increasingly enigmatic. As a group of lipophilic molecules (tocopherols and tocotrienols), vitamin E has been shown to influence the properties of its host membrane, and a wealth of research has connected vitamin E to polyunsaturated fatty acid (PUFA) lipids. Here, we use contrast-matched small-angle neutron scattering and differential scanning calorimetry to integrate these fields by examining the influence of vitamin E on lipid domain stability in PUFA-based lipid mixtures. The influence of α-tocopherol, γ-tocopherol, and α-tocopherylquinone on the lateral organization of a 1:1 lipid mixture of saturated distearoylphosphatidylcholine (DSPC) and polyunsaturated palmitoyl-linoleoylphosphatidylcholine (PLiPC) with cholesterol provides a complement to our growing understanding of the influence of tocopherol on lipid phases. Characterization of domain melting suggests a slight depression in the transition temperature and a decrease in transition cooperativity. Tocopherol concentrations that are an order of magnitude higher than anticipated physiological concentrations (2 mol percent) do not significantly perturb lipid domains; however, addition of 10 mol percent is able to destabilize domains and promote lipid mixing. In contrast to this behavior, increasing concentrations of the oxidized product of α-tocopherol (α-tocopherylquinone) induces a proportional increase in domain stabilization. We speculate how the contrasting effect of the oxidized product may supplement the antioxidant response of vitamin E.

Vitamin E (Alpha-Tocopherol) Metabolism and Nutrition in Chronic Kidney Disease

Vitamin E (alpha-tocopherol) is an essential micronutrient and fat-soluble antioxidant with proposed role in protecting tissues from uncontrolled lipid peroxidation. This vitamin has also important protein function and gene modulation effects. The metabolism of vitamin E depends on hepatic binding proteins that selectively retain food alpha-tocopherol for incorporation into nascent VLDL and tissue distribution together with esterified cholesterol and triglycerides. Chronic kidney disease (CKD) is a condition of oxidative stress and increased lipid peroxidation, that are associated with alterations of alpha-tocopherol metabolism and function. Specific changes have been reported for the levels of its enzymatic metabolites, including both short-chain and long-chain metabolites, the latter being endowed with regulatory functions on enzymatic and gene expression processes important for the metabolism of lipids and xenobiotics detoxification, as well as for the control of immune and inflammatory processes. Vitamin E therapy has been investigated in CKD using both oral vitamin E protocols and vitamin E-coated hemodialyzers, showing promising results in the secondary prevention of cardiovascular disease, as well as of immune and hematological complications. These therapeutic approaches are reviewed in the present article, together with a narrative excursus on the main findings indicating CKD as a condition of relative deficiency and impaired metabolism of vitamin E.

The antioxidant vitamin E as a membrane raft modulator: Tocopherols do not abolish lipid domains

The antioxidant vitamin E is a commonly used vitamin supplement. Although the multi-billion dollar vitamin and nutritional supplement industry encourages the use of vitamin E, there is very little evidence supporting its actual health benefits. Moreover, vitamin E is now marketed as a lipid raft destabilizing anti-cancer agent, in addition to its antioxidant behaviour. Here, we studied the influence of vitamin E and some of its vitamers on membrane raft stability using phase separating unilamellar lipid vesicles in conjunction with small-angle scattering techniques and fluorescence microscopy. We find that lipid phase behaviour remains unperturbed well beyond physiological concentrations of vitamin E (up to a mole fraction of 0.10). Our results are consistent with a proposed line active role of vitamin E at the domain boundary. We discuss the implications of these findings as they pertain to lipid raft modification in native membranes, and propose a new hypothesis for the antioxidant mechanism of vitamin E.

Preparation, optimization, and in-vitro characterization of α-tocopherol-loaded solid lipid nanoparticles (SLNs)

Objective: The main scope of present investigation was preparation and physicochemical characterization of solid lipid nanoparticles (SLNs) loaded by α-tocopherol acetate (ATA).Methods: ATA-loaded nanoparticles were prepared by solvent injection-homogenization technique using stearic acid as the solid lipid, phosphatidylcholine as the stabilizer and finally coated by chitosan with the aim of increasing z-potential and also having a more stable nano-formulation. Then, characterization of SLNs has been conducted using dynamic light scattering (DLS), zeta potential measurement, Fourier transform infrared spectroscopy (FTIR), and differential scanning calorimetry (DSC).Results: Nanoparticles with average sizes of 175 ± 15 nm and zeta potential of +35 ± 2.5 mV were obtained. An excellent drug entrapment efficiency of 90.58 ± 1.38% was obtained with a no-burst slow release up to about 10 days tested. The final plateau of release of ATA from nanoparticulate system within 216 h was 61.13 ± 0.13% which was approached in about 150 h. Physical stability studies showed that the ATA nano-formulation remained stable with slight increase in mean particle size and polydispersity index over a 3-month period in refrigerated temperature. Considering both FTIR and DSC analysis, it can be concluded that there is no new band formation between materials and ATA in our nano-formulation. Particle sizes obtained using AFM images are in a good agreement to those established from the DLS analysis.Conclusion: These data showed a promising delivery system for vitamin E based on SLN platform.

Excitotoxicity, neuroinflammation and oxidant stress as molecular bases of epileptogenesis and epilepsy-derived neurodegeneration: The role of vitamin E

Glutamate-mediated excitotoxicity, neuroinflammation, and oxidative stress are common underlying events in neurodegeneration. This pathogenic "triad" characterizes the neurobiology of epilepsy, leading to seizure-induced cell death, increased susceptibility to neuronal synchronization and network alterations. Along with other maladaptive changes, these events pave the way to spontaneous recurrent seizures and progressive degeneration of the interested brain areas. In vivo models of epilepsy are available to explore such epileptogenic mechanisms, also assessing the efficacy of chemoprevention and therapy strategies at the pre-clinical level. The kainic acid model of pharmacological excitotoxicity and epileptogenesis is one of the most investigated mimicking the chronicization profile of temporal lobe epilepsy in humans. Its pathogenic cues include inflammatory and neuronal death pathway activation, mitochondrial disturbances and lipid peroxidation of several regions of the brain, the most vulnerable being the hippocampus. The importance of neuroinflammation and lipid peroxidation as underlying molecular events of brain damage was demonstrated in this model by the possibility to counteract the related maladaptive morphological and functional changes of this organ with vitamin E, the main fat-soluble cellular antioxidant and "conditional" co-factor of enzymatic pathways involved in polyunsaturated lipid metabolism and inflammatory signaling. The present review paper provides an overview of the literature supporting the potential for a timely intervention with vitamin E therapy in clinical management of seizures and epileptogenic processes associated with excitotoxicity, neuroinflammation and lipid peroxidation, i.e. the pathogenic "triad".

Encapsulation of Vitamin E and Soy Isoflavone Using Spiral Dextrin: Comparative Structural Characterization, Release Kinetics, and Antioxidant Capacity during Simulated Gastrointestinal Tract

Spiral dextrin subfraction (SD-40) obtained through enzyme debranching and gradient ethanol precipitation could interact with vitamin E (VE) or soy isoflavone (SIO) to form V-type inclusion complexes. The formation of two inclusion complexes was confirmed by Fourier transform-infrared spectroscopy, atomic force microscopy, and differential scanning calorimetry. In this study, an in vitro gastrointestinal model was used to investigate the breakdown of inclusion complexes and release behavior of bioactive compounds. The results indicated that the two inclusion complexes exhibited a controlled and sustained release behavior during digestion. In addition, the SD-40/VE inclusion complex presented higher stability and stronger antioxidant capacity than the SD-40/SIO inclusion complex. Furthermore, the first and zero order models were applied to understand the release kinetics of VE and SIO from inclusion complexes in the stomach, whereas the first order model was chosen to describe the release of VE and SIO from inclusion complexes in the intestine.

A Vitamin E-Enriched Antioxidant Diet Interferes with the Acute Adaptation of the Liver to Physical Exercise in Mice

Physical exercise is beneficial for general health and is an effective treatment for metabolic disorders. Vitamin E is widely used as dietary supplement and is considered to improve non-alcoholic fatty liver disease by reducing inflammation and dyslipidemia. However, increased vitamin E intake may interfere with adaptation to exercise training. Here, we explored how vitamin E alters the acute exercise response of the liver, an organ that plays an essential metabolic role during physical activity. Mice fed a control or an α-tocopherol-enriched diet were subjected to a non-exhaustive treadmill run. We assessed the acute transcriptional response of the liver as well as glucocorticoid signalling and plasma free fatty acids (FFA) and performed indirect calorimetry. Vitamin E interfered with the exercise-induced increase in FFA and upregulation of hepatic metabolic regulators, and it shifted the transcriptional profile of exercised mice towards lipid and cholesterol synthesis while reducing inflammation. Energy utilization, as well as corticosterone levels and signalling were similar, arguing against acute differences in substrate oxidation or glucocorticoid action. Our results show that high-dose vitamin E alters the metabolic and inflammatory response of the liver to physical exercise. The interference with these processes may suggest a cautious use of vitamin E as dietary supplement.

Recent developments in d-α-tocopheryl polyethylene glycol-succinate-based nanomedicine for cancer therapy

Cancer remains an obstacle to be surmounted by humans. As an FDA-approved biocompatible drug excipient, d-α-tocopheryl polyethylene glycol succinate (TPGS) has been widely applied in drug delivery system (DDS). Along with in-depth analyses of TPGS-based DDS, increasingly attractive results have revealed that TPGS is able to act not only as a simple drug carrier but also as an assistant molecule with various bio-functions to improve anticancer efficacy. In this review, recent advances in TPGS-based DDS are summarized. TPGS can inhibit P-glycoprotein, enhance drug absorption, induce mitochondrial-associated apoptosis or other apoptotic pathways, promote drug penetration and tumor accumulation, and even inhibit tumor metastasis. As a result, many formulations, by using original TPGS, TPGS-drug conjugates or TPGS copolymers, were prepared, and as expected, an enhanced therapeutic effect was achieved in different tumor models, especially in multidrug resistant and metastatic tumors. Although the mechanisms by which TPGS participates in such functions are not yet very clear, considering its effectiveness in tumor treatment, TPGS-based DDS appears to be one of the best candidates for future clinical applications.

Chain-Breaking Phenolic 2,3-Dihydrobenzo[b]selenophene Antioxidants: Proximity Effects and Regeneration Studies

Phenolic 2,3-dihydrobenzo[b]selenophene antioxidants bearing an OH-group ortho (9), meta (10, 11) and para (8) to the Se were prepared by seleno-Claisen rearrangement/intramolecular hydroselenation. meta-Isomer (11) was studied by X-ray crystallography. The radical-trapping activity and regenerability of compounds 8-11 were evaluated using a two-phase system in which linoleic acid was undergoing peroxidation in the lipid phase while regeneration of the antioxidant by co-antioxidants (N-acetylcysteine, glutathione, dithiothreitol, ascorbic acid, tris(carboxyethyl)phosphine hydrochloride) was ongoing in the aqueous layer. Compound 9 quenched peroxyl radicals more efficiently than α-tocopherol. It also provided the most long-lasting antioxidant protection. With thiol co-antioxidants it could inhibit peroxidation for more than five-fold longer than the natural product. Regeneration was more efficient when the aqueous phase pH was slightly acidic. Since calculated O-H bond dissociation energies for 8-11 were substantially larger than for α-tocopherol, an antioxidant mechanism involving O-atom transfer from peroxyl to selenium was proposed. The resulting phenolic selenoxide/alkoxyl radical would then exchange a hydrogen atom in a solvent cage before antioxidant regeneration at the aqueous lipid interphase.

Comparative Structural Characterization of Spiral Dextrin Inclusion Complexes with Vitamin E or Soy Isoflavone

In this study, the preparation and structural properties of spiral dextrin (SD)/vitamin E and SD/soy isoflavone inclusion complexes were studied. SD was obtained from debranched normal maize starch using isoamylases. After fractionation using a novel method of gradient ethanol precipitation, SD was separated into different fractions, among which SD-40 was found to be the optimal host molecule to prepare SD inclusion complexes with vitamin E or soy isoflavone. X-ray diffraction (XRD) and 13C cross-polarization magic angle spinning nuclear magnetic resonance (NMR) suggested that the crystalline structures of SD-40/vitamin E and SD-40/soy isoflavone were V6II and V6III types, respectively. Small-angle X-ray scattering revealed that the SD-40/vitamin E inclusion complex formed a tighter and more compact crystallite than the SD-40/soy isoflavone inclusion complex. Furthermore, the connection structures of inclusion complexes were investigated by two-dimensional nuclear Overhauser effect spectroscopy NMR, indicating that part of vitamin E with an alkyl chain was encapsulated in the helix cavity of SD-40, whereas the aromatic ring B of the soy isoflavone molecule was complexed by the helix cavity and screw of SD.

Free-radicals and advanced chemistries involved in cell membrane organization influence oxygen diffusion and pathology treatment

A breakthrough has been discovered in pathology chemistry related to increasing molecular structure that can interfere with oxygen diffusion through cell membranes. Free radicals can crosslink unsaturated low-viscosity fatty acid oils by chain-growth polymerization into more viscous liquids and even solids. Free radicals are released by mitochondria in response to intermittent hypoxia that can increase membrane molecular organization to reduce fluidity and oxygen diffusion in a possible continuing vicious cycle toward pathological disease. Alternate computational chemistry demonstrates molecular bond dynamics in free energy for cell membrane physiologic movements. Paired electrons in oxygen and nitrogen atoms require that oxygen bonds rotate and nitrogen bonds invert to seek polar nano-environments and hide from nonpolar nano-environments thus creating fluctuating instability at a nonpolar membrane and polar biologic fluid interface. Subsequent mechanomolecular movements provide free energy to increase diffusion by membrane transport of molecules and oxygen into the cell, cell-membrane signaling/recognition/defense in addition to protein movements for enzyme mixing. In other chemistry calcium bonds to membrane phosphates primarily on the outer plasma cell membrane surface to influence the membrane firing threshold for excitability and better seal out water permeation. Because calcium is an excellent metal conductor and membrane phosphate headgroups form a semiconductor at the biologic fluid interface, excess electrons released by mitochondria may have more broad dissipation potential by safe conduction through calcium atomic-sized circuits on the outer membrane surface. Regarding medical conditions, free radicals are known to produce pathology especially in age-related disease in addition to aging. Because cancer cell membranes develop extreme polymorphism that has been extensively followed in research, accentuated easily-visualized free-radical models are developed. In terms of treatment, use of vitamin nutrient supplements purported to be antioxidants that remove free radicals has not proved worthwhile in clinical trials presumably due to errors with early antioxidant measurements based on inaccurate colorimetry tests. However, newer covalent-bond shrinkage tests now provide accurate measurements for free-radical inhibitor hydroquinone and other molecules toward drug therapy.

Horizontal alignment of 5' -> 3' intergene distance segment tropy with respect to the gene as the conserved basis for DNA transcription

AIM

To study the conserved basis for gene expression in comparative cell types at opposite ends of the cell pressuromodulation spectrum, the lymphatic endothelial cell and the blood microvascular capillary endothelial cell.

METHODS

The mechanism for gene expression is studied in terms of the 5' -> 3' direction paired point tropy quotients (prpT_Qs) and the final 5' -> 3' direction episodic sub-episode block sums split-integrated weighted average-averaged gene overexpression tropy quotient (esebssiwaagoT_Q).

RESULTS

The final 5' -> 3' esebssiwaagoT_Q classifies an lymphatic endothelial cell overexpressed gene as a supra-pressuromodulated gene (esebssiwaagoT_Q ≥ 0.25 < 0.75) every time and classifies a blood microvascular capillary endothelial cell overexpressed gene every time as an infra-pressuromodulated gene (esebssiwaagoT_Q < 0.25) (100% sensitivity; 100% specificity).

CONCLUSION

Horizontal alignment of 5' -> 3' intergene distance segment tropy wrt the gene is the basis for DNA transcription in the pressuromodulated state.

Vitamin E: Emerging aspects and new directions

The discovery of vitamin E will have its 100th anniversary in 2022, but we still have more questions than answers regarding the biological functions and the essentiality of vitamin E for human health. Discovered as a factor essential for rat fertility and soon after characterized for its properties of fat-soluble antioxidant, vitamin E was identified to have signaling and gene regulation effects in the 1980s. In the same years the cytochrome P-450 dependent metabolism of vitamin E was characterized and a first series of studies on short-chain carboxyethyl metabolites in the 1990s paved the way to the hypothesis of a biological role for this metabolism alternative to vitamin E catabolism. In the last decade other physiological metabolites of vitamin E have been identified, such as α-tocopheryl phosphate and the long-chain metabolites formed by the ω-hydroxylase activity of cytochrome P-450. Recent findings are consistent with gene regulation and homeostatic roles of these metabolites in different experimental models, such as inflammatory, neuronal and hepatic cells, and in vivo in animal models of acute inflammation. Molecular mechanisms underlying these responses are under investigation in several laboratories and side-glances to research on other fat soluble vitamins may help to move faster in this direction. Other emerging aspects presented in this review paper include novel insights on the mechanisms of reduction of the cardiovascular risk, immunomodulation and antiallergic effects, neuroprotection properties in models of glutamate excitotoxicity and spino-cerebellar damage, hepatoprotection and prevention of liver toxicity by different causes and even therapeutic applications in non-alcoholic steatohepatitis. We here discuss these topics with the aim of stimulating the interest of the scientific community and further research activities that may help to celebrate this anniversary of vitamin E with an in-depth knowledge of its action as vitamin.

Oxidative stress and antioxidants: Distress or eustress?

There is a growing consensus that reactive oxygen species (ROS) are not just associated with various pathologies, but that they act as physiological redox signaling messenger with important regulatory functions. It is sometimes stated that "if ROS is a physiological signaling messenger, then removal of ROS by antioxidants such as vitamins E and C may not be good for human health." However, it should be noted that ROS acting as physiological signaling messenger and ROS removed by antioxidants are not the same. The lipid peroxidation products of polyunsaturated fatty acids and cholesterol induce adaptive response and enhance defense capacity against subsequent oxidative insults, but it is unlikely that these lipid peroxidation products are physiological signaling messenger produced on purpose. The removal of ROS and inhibition of lipid peroxidation by antioxidants should be beneficial for human health, although it has to be noted also that they may not be an effective inhibitor of oxidative damage mediated by non-radical oxidants. The term ROS is vague and, as there are many ROS and antioxidants which are different in chemistry, it is imperative to explicitly specify ROS and antioxidant to understand the effects and role of oxidative stress and antioxidants properly.

Antioxidants as therapeutics in the intensive care unit: Have we ticked the redox boxes?

Critically ill patients are under oxidative stress and antioxidant administration reasonably emerged as a promising approach to combat the aberrant redox homeostasis in this patient cohort. However, the results of the antioxidant treatments in the intensive care unit are conflicting and inconclusive. The main objective of the present review is to highlight some inherent, yet widely overlooked redox-related issues about the equivocal effectiveness of antioxidants in the intensive care unit, beyond methodological considerations. In particular, the discrepancy in the literature partially stems from: (1) the largely unspecified role of reactive species in disease onset and progression, (2) our fragmentary understanding on the interplay between inflammation and oxidative stress, (3) the complex spatiotemporal specificity of in vivo redox biology, (4) the pleiotropic effects of antioxidants and (5) the divergent effects of antioxidants according to the temporal administration pattern. In addition, two novel and sophisticated practices with promising pre-clinical results are presented: (1) the selective neutralization of reactive species in key organelles after they are formed (i.e., in mitochondria) and (2) the targeted complete inhibition of dominant reactive species sources (i.e., NADPH oxidases). Finally, the reductive potential of NADPH as a key pharmacological target for redox therapies is rationalized. In light of the above, the recontextualization of knowledge from basic redox biology to translational medicine seems imperative to perform more realistic in vivo studies in the fast-growing field of critical care pharmacology.

The Use of Liprotides To Stabilize and Transport Hydrophobic Molecules

Recently, it has been shown that different complexes consisting of protein and fatty acids, which we call liprotides, have common functional and structural features. Liprotides can transfer their fatty acid content to membranes, highlighting the potential to incorporate other small molecules and help transfer them to membranes. In this study, this potential was explored with regard to the poorly water-soluble vitamin E compound α-tocopherol (Toc). Uptake into liprotides increased Toc solubility and chemical stability. The liprotide-Toc complexes retained the characteristic liprotide structure with a core of fatty acid surrounded by protein. Toc and fatty acid could be transferred to artificial vesicles upon being incorporated into the liprotide complex. Extending this work, we found that free tryptophan and the vitamin A precursor retinaldehyde could also be incorporated in the liprotides; however, other small molecules failed to be taken up, and we conclude that successful incorporation requires a hydrophobic terminal moiety that can be accommodated within the micelle interior of the liprotides. Nevertheless, our work suggests that liprotides are able to stabilize and transport a number of otherwise insoluble small molecules with significant potential health benefits.

Enhancing vitamin E bioaccessibility: factors impacting solubilization and hydrolysis of α-tocopherol acetate encapsulated in emulsion-based delivery systems

Impact of free fatty acid chain length on vitamin E bioaccessibility: long chain FFAs form mixed micelles that easily accommodate vitamin E, whereas medium chain FFAs do not.

Reaction rates of α-tocopheroxyl radicals confined in micelles and in human plasma lipoproteins

α-Tocopherol, the main component of vitamin E, traps highly reactive radicals which otherwise might react with lipids present in plasmatic lipoproteins or in cell membranes. The α-tocopheroxyl radicals generated by this process have also a pro-oxidant action which is contrasted by their reaction with ascorbate or by bimolecular self-reaction (dismutation). The kinetics of this bimolecular self-reaction were explored in solution such as ethanol, and in heterogeneous systems such as deoxycholic acid micelles and in human plasma. According to ESR measurements, the kinetic rate constant (2k(d)) of the bimolecular self-reaction of α-tocopheroxyl radicals in micelles and in human plasma was calculated to be of the order of 10(5) M(-1) s(-1) at 37 °C. This value was obtained considering that the reactive radicals are confined into the micellar pseudophase and is one to two orders of magnitude higher than the value we found in homogeneous phase. The physiological significance of this high value is discussed considering the competition between bimolecular self-reaction and the α-tocopheroxyl radical recycling by ascorbate.

Vitamin E and vitamin E acetate solubilization in mixed micelles: physicochemical basis of bioaccessibility

Vitamin E is an essential micronutrient for humans and animals due to its antioxidant and non-antioxidant biological activities. In this study, an emulsion titration assay was used to quantify the kinetics and extent of vitamin E and vitamin E acetate solubilization in model mixed micelles. The composition of the mixed micelles was designed to mimic those produced during digestion of lipids in the human small intestine: bile salts, phospholipids, and free fatty acids. Initially, the optimum conditions required to form model mixed micelles were established. The solubilization capacities of vitamin E and vitamin E acetate in the mixed micelles were then compared. The solubilization capacity of the mixed micelles for vitamin E was higher than that for vitamin E acetate, which was attributed to differences in the ability of the vitamin molecules to be incorporated into the micelle structure. The solubilization capacities also depended on the composition of the mixed micelles: micelle solubilization of vitamin E was increased by the presence of phospholipid (DOPC), but did not depend strongly on the presence of free fatty acid (octanoic acid or linoleic acid). Overall, this research has important implications for understanding the digestion, absorption, and transportation of vitamin E in the human gastrointestinal tract and for designing suitable delivery systems to increase its bioaccessibility.

Tocopherol activity correlates with its location in a membrane: a new perspective on the antioxidant vitamin E

We show evidence of an antioxidant mechanism for vitamin E which correlates strongly with its physical location in a model lipid bilayer. These data address the overlooked problem of the physical distance between the vitamin's reducing hydrogen and lipid acyl chain radicals. Our combined data from neutron diffraction, NMR, and UV spectroscopy experiments all suggest that reduction of reactive oxygen species and lipid radicals occurs specifically at the membrane's hydrophobic-hydrophilic interface. The latter is possible when the acyl chain "snorkels" to the interface from the hydrocarbon matrix. Moreover, not all model lipids are equal in this regard, as indicated by the small differences in vitamin's location. The present result is a clear example of the importance of lipid diversity in controlling the dynamic structural properties of biological membranes. Importantly, our results suggest that measurements of aToc oxidation kinetics, and its products, should be revisited by taking into consideration the physical properties of the membrane in which the vitamin resides.

Glutathione peroxidases

BACKGROUND

With increasing evidence that hydroperoxides are not only toxic but rather exert essential physiological functions, also hydroperoxide removing enzymes have to be re-viewed. In mammals, the peroxidases inter alia comprise the 8 glutathione peroxidases (GPx1-GPx8) so far identified.

SCOPE OF THE REVIEW

Since GPxs have recently been reviewed under various aspects, we here focus on novel findings considering their diverse physiological roles exceeding an antioxidant activity.

MAJOR CONCLUSIONS

GPxs are involved in balancing the H2O2 homeostasis in signalling cascades, e.g. in the insulin signalling pathway by GPx1; GPx2 plays a dual role in carcinogenesis depending on the mode of initiation and cancer stage; GPx3 is membrane associated possibly explaining a peroxidatic function despite low plasma concentrations of GSH; GPx4 has novel roles in the regulation of apoptosis and, together with GPx5, in male fertility. Functions of GPx6 are still unknown, and the proposed involvement of GPx7 and GPx8 in protein folding awaits elucidation.

GENERAL SIGNIFICANCE

Collectively, selenium-containing GPxs (GPx1-4 and 6) as well as their non-selenium congeners (GPx5, 7 and 8) became key players in important biological contexts far beyond the detoxification of hydroperoxides. This article is part of a Special Issue entitled Cellular functions of glutathione.

Vitamin E-derived copolymers continue the challenge to hemodialysis biomaterials

Improving material biocompatibility has been a continuous effort and remains a major goal of dialysis therapy. In this respect, vitamin E-modified copolymers have been used to produce a generation of biomaterials that has offered new clinical challenges and the chance of further improving the quality of synthetic hemodialyser membranes. This mini review article describes the evolution of these copolymers that only recently have been adopted to develop new vitamin E-modified polysulfone hemodialysers. Biomaterial characteristics and clinical aspects of these membranes are discussed, starting from the most recent contributions that have appeared in the literature that are of interest for the community of nephrology and dialysis specialists, as well as biomaterial scientists.

Vitamins

• Based on strong research evidence, all infants should receive 400 IU/day of vitamin D beginning in the first few days of age to prevent vitamin D deficiency and rickets. • Based on strong research evidence, children and adolescents age >1 year may require as much as 600IU/day of vitamin D. • Based on strong research evidence, all newborns should receive 1 mg of vitamin K at birth to prevent vitamin K deficiency bleeding. • Based on strong research evidence, preconceptional and pregnant women should be supplemented with folate to decrease the likelihood of neural tube defects.

Redox biology of exercise: an integrative and comparative consideration of some overlooked issues

The central aim of this review is to address the highly multidisciplinary topic of redox biology as related to exercise using an integrative and comparative approach rather than focusing on blood, skeletal muscle or humans. An attempt is also made to re-define ‘oxidative stress’ as well as to introduce the term ‘alterations in redox homeostasis’ to describe changes in redox homeostasis indicating oxidative stress, reductive stress or both. The literature analysis shows that the effects of non-muscle-damaging exercise and muscle-damaging exercise on redox homeostasis are completely different. Non-muscle-damaging exercise induces alterations in redox homeostasis that last a few hours post exercise, whereas muscle-damaging exercise causes alterations in redox homeostasis that may persist for and/or appear several days post exercise. Both exhaustive maximal exercise lasting only 30 s and isometric exercise lasting 1–3 min (the latter activating in addition a small muscle mass) induce systemic oxidative stress. With the necessary modifications, exercise is capable of inducing redox homeostasis alterations in all fluids, cells, tissues and organs studied so far, irrespective of strains and species. More importantly, ‘exercise-induced oxidative stress’ is not an ‘oddity’ associated with a particular type of exercise, tissue or species. Rather, oxidative stress constitutes a ubiquitous fundamental biological response to the alteration of redox homeostasis imposed by exercise. The hormesis concept could provide an interpretative framework to reconcile differences that emerge among studies in the field of exercise redox biology. Integrative and comparative approaches can help determine the interactions of key redox responses at multiple levels of biological organization.

γ-Tocopherol inhibits human prostate cancer cell proliferation by up-regulation of transglutaminase 2 and down-regulation of cyclins

To establish a system to study differentiation therapy drugs, we used the androgen-independent human prostate PC-3 tumor cell line as a target and α- and γ-tocopherol as inducers. Effects of α- and γ-tocopherol on the cell cycle, proliferation and differentiation, were examined. A more significant growth inhibition activity for γ- than for α-tocopherol was observed. Flow cytometry analysis of α- and γ-tocopherol-treated prostate carcinoma PC3 cells showed decreased progression into the S-phase. This effect, particularly evident for γ-tocopherol, was associated with an up-regulation and increased activity of transglutaminase 2 (TG2), a reduced DNA synthesis and a remarkable decreased levels of cyclin D1 and cyclin E. Activation of TG2 suggests that γ-tocopherol has an evident differentiative capacity on PC3 cells, leading to an increased expression of TG2, and reduced cyclin D1 and cyclin E levels, affecting cell cycle progression. It is feasible that up-regulation and activation of TG2, associated with a reduced proliferation, are parts of a large-scale reprogramming that can attenuate the malignant phenotype of PC3 cells in vitro. These data suggest further investigation on the potential use of this γ-form of vitamin E as a differentiative agent, in combination with the common cytotoxic treatments for prostate cancer therapy.

Conjugate addition of isocyanides to chromone 3-carboxylic acid: an efficient one-pot synthesis of chroman-4-one 2-carboxamides

We report a novel Lewis acid catalysed tandem reaction of isocyanides, chromone 3-carboxylic acid and nucleophiles. An experimentally very simple procedure, involving the use of microwave irradiation in the presence of a Lewis acid catalyst, affords a representative collection of chromone-2-carboxamides and chromone-2-carboxamido-3-esters in high yields, in just a few minutes. Such an unprecedented strategy is formally equivalent to a conjugate addition of isocyanides to Michael acceptors.

Synthetic chromanol derivatives and their interaction with complex III in mitochondria from bovine, yeast, and Leishmania

Synthetic chromanol derivatives (TMC4O, 6-hydroxy-2,2,7,8-tetramethyl-chroman-4-one; TMC2O, 6-hydroxy-4,4,7,8-tetramethyl-chroman-2-one; and Twin, 1,3,4,8,9,11-hexamethyl-6,12-methano-12H-dibenzo[d,g][1,3]dioxocin-2,10-diol) share structural elements with the potent inhibitor of the mitochondrial cytochrome (cyt) bc(1) complex stigmatellin. Studies with isolated bovine cyt bc(1) complex demonstrated that these compounds partially inhibit the mammalian enzyme. The aim of this work was to comparatively investigate these toxicological aspects of synthetic vitamin E derivatives in mitochondria of different species. The chromanols and atovaquone as reference compound were evaluated for their inhibition of the cyt bc(1) activity in mitochondrial fractions from bovine hearts, yeast, and Leishmania. In addition, compounds were evaluated in vitro for their inhibitory activity against whole-cell Leishmania and mouse peritoneal macrophages. In these organisms, the chromanols showed a species-selective inhibition of the cyt bc(1) activity different from that of atovaquone. While in atovaquone the side chain mediates species-selectivity, the marked differences for TMC2O and TMC4O in cyt bc(1) inhibition suggests that direct substitution of the chromanol headgroup will control selectivity in these compounds. Low micromolar concentrations of TMC2O (IC(50) = 9.5 ± 0.5 μM) inhibited the growth of Leishmania, and an esterified TMC2CO derivative inhibited the cyt bc(1) activity with an IC(50) of 4.9 ± 0.9 μM. These findings suggest that certain chromanols also exhibit beyond their antioxidative properties antileishmanial activities and that TMC2O derivatives could be useful toward the development of highly active antiprotozoal compounds.

Novel tocopherol derivatives. Part 32: On the bromination of pyrano[3,2-f]chromenes related to γ-tocopherol

While bromination of γ-tocopherol (2) with elemental bromine affords 5-bromo-γ-tocopherol quantitatively (3), the analogous reaction of its truncated model compound, 2,2,7,8-tetramethylchromanol (2a) is known to be accompanied by side reactions and to produce hitherto unknown byproducts. These compounds originate from pyrano[3,2-f]chromene (6), a byproduct in the synthesis of model compound 2a, which affords bromochromene 7 as the major product. The reaction mechanism was shown to proceed via chromene 8 and its 1,2-dibromo addition compound 9, which eliminates HBr in an E1 process to finally afford 7. Analytical data including crystal structures of both 6 and 7 are reported.

No effect of antioxidant supplementation on muscle performance and blood redox status adaptations to eccentric training

BACKGROUND

It was recently reported that antioxidant supplementation decreases training efficiency and prevents cellular adaptations to chronic exercise.

OBJECTIVE

This study aimed to investigate the effects of vitamin C and vitamin E supplementation on muscle performance, blood and muscle redox status biomarkers, and hemolysis in trained and untrained men after acute and chronic exercise. A specific type of exercise was applied (eccentric) to produce long-lasting and extensive changes in redox status biomarkers and to examine more easily the potential effects of antioxidant supplementation.

DESIGN

In a double-blinded fashion, men received either a daily oral supplement of vitamin C and vitamin E (n = 14) or placebo (n = 14) for 11 wk (started 4 wk before the pretraining exercise testing and continued until the posttraining exercise testing). After baseline testing, the subjects performed an eccentric exercise session 2 times/wk for 4 wk. Before and after the chronic eccentric exercise, the subjects underwent one session of acute eccentric exercise, physiologic measurements were performed, and blood samples and muscle biopsy samples (from 4 men) were collected.

RESULTS

The results failed to support any effect of antioxidant supplementation. Eccentric exercise similarly modified muscle damage and performance, blood redox status biomarkers, and hemolysis in both the supplemented and nonsupplemented groups. This occurred despite the fact that eccentric exercise induced marked changes in muscle damage and performance and in redox status after exercise.

CONCLUSION

The complete lack of any effect on the physiologic and biochemical outcome measures used raises questions about the validity of using oral antioxidant supplementation as a redox modulator of muscle and redox status in healthy humans.

Biomarkers in natural fish populations indicate adverse biological effects of offshore oil production

Background

Despite the growing awareness of the necessity of a sustainable development, the global economy continues to depend largely on the consumption of non-renewable energy resources. One such energy resource is fossil oil extracted from the seabed at offshore oil platforms. This type of oil production causes continuous environmental pollution from drilling waste, discharge of large amounts of produced water, and accidental spills.

Methods and principal findings

Samples from natural populations of haddock (Melanogrammus aeglefinus) and Atlantic cod (Gadus morhua) in two North Sea areas with extensive oil production were investigated. Exposure to and uptake of polycyclic aromatic hydrocarbons (PAHs) were demonstrated, and biomarker analyses revealed adverse biological effects, including induction of biotransformation enzymes, oxidative stress, altered fatty acid composition, and genotoxicity. Genotoxicity was reflected by a hepatic DNA adduct pattern typical for exposure to a mixture of PAHs. Control material was collected from a North Sea area without oil production and from remote Icelandic waters. The difference between the two control areas indicates significant background pollution in the North Sea.

Conclusion

It is most remarkable to obtain biomarker responses in natural fish populations in the open sea that are similar to the biomarker responses in fish from highly polluted areas close to a point source. Risk assessment of various threats to the marine fish populations in the North Sea, such as overfishing, global warming, and eutrophication, should also take into account the ecologically relevant impact of offshore oil production.