Interactions of tocopherols and ubiquinones with monolayers of phospholipids

Effect of Ester Moiety on Structural Properties of Binary Mixed Monolayers of Alpha-Tocopherol Derivatives with DPPC

Phospholipid membranes are ubiquitous components of cells involved in physiological processes; thus, knowledge regarding their interactions with other molecules, including tocopherol ester derivatives, is of great importance. The surface pressure–area isotherms of pure α-tocopherol (Toc) and its derivatives (oxalate (OT), malonate (MT), succinate (ST), and carbo analog (CT)) were studied in Langmuir monolayers in order to evaluate phase formation, compressibility, packing, and ordering. The isotherms and compressibility results indicate that, under pressure, the ester derivatives and CT are able to form two-dimensional liquid-condensed (LC) ordered structures with collapse pressures ranging from 27 mN/m for CT to 44 mN/m for OT. Next, the effect of length of ester moiety on the surface behavior of DPPC/Toc derivatives’ binary monolayers at air–water interface was investigated. The average molecular area, elastic modulus, compressibility, and miscibility were calculated as a function of molar fraction of derivatives. Increasing the presence of Toc derivatives in DPPC monolayer induces expansion of isotherms, increased monolayer elasticity, interrupted packing, and lowered ordering in monolayer, leading to its fluidization. Decreasing collapse pressure with increasing molar ratio of derivatives indicates on the miscibility of Toc esters in DPPC monolayer. The interactions between components were analyzed using additivity rule and thermodynamic calculations of excess and total Gibbs energy of mixing. Calculated excess area and Gibbs energy indicated repulsion between components, confirming their partial mixing. In summary, the mechanism of the observed phenomena is mainly connected with interactions of ionized carboxyl groups of ester moieties with DPPC headgroup moieties where formed conformations perturb alignment of acyl chains, resulting in increasing mean area per molecule, leading to disordering and fluidization of mixed monolayer.

Miscibility of dl-α-tocopherol β-glucoside in DPPC monolayer at air/water and air/solid interfaces

The role of newly synthesized tocopherol glycosidic derivative in modifying molecular organization and phase transitions of phospholipid monolayer at the air/water interface has been investigated. Two-component Langmuir films of dl-α-tocopheryl β-D-glucopyranoside (BG) mixed with dipalmitoyl phosphatidylcholine (DPPC) in the whole range of mole fractions were formed at the water surface. An analysis of surface pressure versus mean molecular area (π-A) isotherms and Brewster angle microscope images showed that the presence of BG molecules changes the structure and packing of the DPPC monolayer in a BG concentration dependent manner. BG molecules incorporated into DPPC monolayer inhibit its liquid expanded to liquid condensed phase transition proportionally to the BG concentration. The monolayers were also transferred onto solid substrates and visualized using an atomic force microscope. The results obtained indicate almost complete miscibility of BG and DPPC in the monolayers at surface pressures present in the biological cell membrane (30-35·10(-3) N·m(-1)) for a BG mole fraction as high as 0.3. This makes the monolayer less packed and more disordered, leading to an increased permeability. The results support our previous molecular dynamics simulation data.

The location and behavior of alpha-tocopherol in membranes

Vitamin E (alpha-tocopherol) has long been recognized as the major antioxidant in biological membranes, and yet many structurally related questions persist of how the vitamin functions. For example, the very low levels of alpha-tocopherol reported for whole cell extracts question how this molecule can successfully protect the comparatively enormous quantities of PUFA-containing phospholipids found in membranes that are highly susceptible to oxidative attack. The contemporary realization that membranes laterally segregate into regions of distinct lipid composition (domains), we propose, provides the answer. We hypothesize alpha-tocopherol partitions into domains that are enriched in polyunsaturated phospholipids, amplifying the concentration of the vitamin in the place where it is most needed. These highly disordered domains depleted in cholesterol are analogous, but organizationally antithetical, to the well-studied lipid rafts. We review here the ideas that led to our hypothesis. Experimental evidence in support of the formation of PUFA-rich domains in model membranes is presented, focusing upon docosahexaenoic acid that is the most unsaturated fatty acid commonly found. Physical methodologies are then described to elucidate the nature of the interaction of alpha-tocopherol with PUFA and to establish that the vitamin and PUFA-containing phospholipids co-localize in non-raft domains.

Vitamin E as an antioxidant in vitro and in vivo

Measurements of the absolute rate constants for the reaction with peroxyl radicals of alpha, beta, gamma and delta-tocopherol and several model compounds are described. The peroxyl radicals were obtained either by the autoxidation of styrene or by the flash photolysis of di-t-butyl ketone in an oxygen-saturated environment. The kinetic data are discussed in stereoelectronic terms. Vitamin E and total lipid-soluble, chain-breaking antioxidant concentrations in some normal and cancerous tissues have been measured. In human blood plasma and erythrocyte ghost membranes vitamin E is the major, and possibly the only, chain-breaking antioxidant. Lipid extracts of Novikoff ascites hepatoma cells contain considerably more vitamin E relative to lipid than do extracts of normal rat liver. These tumour lipids contain relatively fewer highly unsaturated fatty acids and are present at lower lipid/wet tissue ratios than the normal liver lipids. A number of unresolved problems relating to the action of vitamin E in vivo are discussed.

A theoretical investigation on the geometry and vibrational spectra of 10,10,2,6,5-pentamethyl-1-hydroxychroman: a model of alpha-tocopherol

In the present study, density functional theory calculations with the combined Becke's three-parameter exchange functional in combination with the Lee, Yang, and Parr correlation functional (B3LYP) exchange-correlation energy functions were performed by using the 6-311G** basis set to study the structure and vibrational spectra of 10,10,2,6,5-pentamethyl-1-hydroxychroman (a model of alpha-tocopherol). The fully optimized geometry of the molecule was found to be very consistent with the X-ray crystal structure. The predicted vibrational frequencies made it possible to give a reliable assignment of the IR spectrum of the molecule according to the potential energy distributions (PEDs).

Molecular associations of vitamin E

To understand how vitamin E fulfills its functions in membranes and lipoproteins, it is necessary to know how it associates with the lipid components of these structures and the effects its presence has on their structure and stability. Studies of model membrane systems containing vitamin E have proved to be an informative approach to address these questions. A review of the way vitamin E interacts with phospholipid bilayers, how it distributes within the structure, its motional diffusion characteristics, and orientation has been undertaken. The effect of vitamin E on membrane stability and permeability has been described. The tendency of vitamin E to form complexes with certain phospholipids is examined as is the way modulation of protein functions takes place. Finally, recent evidence relevant to the putative role of vitamin E in protecting membranes from free radical attack and the consequences of lipid oxidation in lipoproteins and membranes is examined.

Linoleate supplementation in steers modifies lipid composition of plasma lipoproteins but does not alter their fluidity

The health value for man of lipids in bovine muscles can be improved by the addition of PUFA to the animals' diets, but such treatments can modify fluidity of plasma lipoproteins and therefore their metabolic functions. The aim of the present study was to analyse whether changes in chemical composition of lipoproteins in steers fed sunflower oil-rich diets altered lipoprotein fluidity, measured by fluorescence polarization and electron spin resonance. LDL, light HDL and heavy HDL fractions were isolated by ultracentrifugation from plasma of eighteen crossbred Charolais×Salers steers. For a period of 70d, animals were given a control diet (C,n6) consisting of hay (540g/kg) and concentrate mixture (460g/kg) or the same basal diet supplemented with sunflower oil rich inn-6 PUFA (40g/kg diet DM), given either as crushed seeds (S,n6) or as a free oil infused directly into the duodenum (O,n6), thus avoiding ruminal hydrogenation of PUFA. We have shown that in bovine animals: (1) fluidity measurements by fluorescence polarization must be made at the bovine physiological temperature (38·5°C); (2) heavy HDL always appear as the less fluid lipoparticles; (3) electron spin resonance, which does not depend on lipoparticle size, is more appropriate to compare the fluidity of LDL with that of light HDL. The values for lipoprotein fluidity measured by both methods indicated that linoleate-rich diets did not have any effect when compared with diet C; however, chemical variables support a fluidification of lipoparticles, since in steers given the diet O,n-6 PUFA concentrations increased in polar (×1·8) and neutral (×1·6) lipids in lipoparticles (P=0·0001). The phospholipid:protein ratio increased in light (+20%,P=0·019) and heavy (+23%,P=0·06) HDL and especially in LDL (+46%,P=0·0001); the total cholesterol:phospholipid ratio decreased in the three lipoprotein classes (−15 to −30%, NS). Diet S led to similar but less pronounced effects. We concluded that linoleate-rich diets modified the chemical composition of plasma lipoproteins in steers, but did not alter their fluidity; this probably occurred as a result of ‘homeoviscous adaptation’, which ensured their functional capacity.

Age-dependent telomere-shortening is repressed by phosphorylated α-tocopherol together with cellular longevity and intracellular oxidative-stress reduction in human brain microvascular endotheliocytes

Cellular life-span of neonatal human brain microvascular endotheliocytes (HBME) was estimated by population doubling levels (PDLs) for serial subcultivations until spontaneous proliferation stoppage, and was 2.4-fold longer for continuous administration with the 6-O-phosphorylated derivative (TocP) of alpha-tocopherol (Toc), being bio-available owing to its water-solubility, or TocP plus 2-O-phosphorylated ascorbate (Asc2P), and 1.3-fold longer with Asc2P, at a dose of 150 microM, than for the non-administered control. Enlarged cell diameters indicative of cellular aging were repressed for TocP-administered cells as analyzed with a channelizer. Age-dependent shortening of telomeric DNA length (291 bp/PDL) was slowed markedly for TocP (165 bp/PDL) or TocP plus Asc2P, but slightly for Asc2P. Telomerase activity as assessed by the PCR-based TRAP method was detectable slightly at younger ages but no longer at middle ages for the non-administered cells, but, for TocP-administered cells, was intensely detected at younger ages and appreciably until middle ages. Intracellular TocP amounts were not changed age-dependently in contrast to a marked decrease in Toc which accrued from TocP esterolysis. This may be partly attributed to age-dependent changes in the lipid peroxidation product acrolein (ACR), which was abundant at older ages in non-administered cells, but scarcely in TocP-administered cells. Furthermore, intracellular reactive oxygen species (ROS) such as H(2)O(2) and hydroperoxides as detected using the redox indicator CDCFH-DA was less abundant in TocP-administered cells than in non-administered cells. Thus the telomeric-DNA retention, concurrently with retained telomerase activity, was shown to be correlated with cellular longevity, and may be supported by diminished oxidative stress, in hydrophobic microenvironment, which can be achieved by TocP rather than AscP.

Pro-oxidative versus antioxidative reactions between Trolox and Cr(VI): The role of H(2)O(2)

The effect of the Vitamin E model compound Trolox in reactions with Cr(VI) in the presence or absence of hydrogen peroxide was investigated. The aim of this study was to establish and discuss potential Trolox-mediated pro-oxidative reactions. The importance of the Trolox:Cr(VI) ratio in the Cr(VI) reduction process was determined from the EPR spectra and DNA cleavage reactions. In the absence of hydrogen peroxide, reduction of Cr(VI) occurred with concomitant oxidation of Trolox to the phenoxyl radical. In the presence of hydrogen peroxide, Cr(V), produced by the reduction of Cr(VI), reduced hydrogen peroxide to the hydroxyl radical. The latter was detected by spin-trapping the methyl radical following reaction with N-methyl sulfoxide. During Cr(VI) reduction with Trolox, DNA single- or double-strand breaks due to Trolox radical formation were not observed. Relaxed DNA appeared only when H(2)O(2) was added to Trolox/Cr(VI) mixtures most probably due to hydroxyl radical formation during the redox cycling of Cr(V/IV)-species. Fenton-like reactions do not play a significant role in the Trolox/Cr(VI) system in the absence of added H(2)O(2).

Impedance Analysis of Phosphatidylcholine/α-Tocopherol System in Bilayer Lipid Membranes

The effect of alpha-tocopherol on the electrochemical features of the phosphatidylcholine membrane was investigated by impedance spectroscopy. Phosphatidylcholine and alpha-tocopherol were chosen for the study because they are present in biological membranes and they fulfill essential functions in living organisms. The experimental impedance values obtained in the presence of different amounts of alpha-tocopherol showed evidence of domain structures within the bilayer containing less than 0.048 molar fraction of alpha-tocopherol. Based on derived mathematical equations, the surface area of phospholipid/alpha-tocopherol domain was calculated; it amounts to 832 A(2). This value is consistent, taking into consideration ordering and condensation effects of alpha-tocopherol, with the acknowledged, well documented, stoichiometry of such a domain of 10:1. The result of the investigation is the proposal of a new method for the determination of the surface area and description of the stoichiometry of domains formed in any two-component system.

The protective effect and mechanism of soybean oil and its extracts on DNA damage in human ECV304 cells exposed to UV-C

The degree of DNA damage in the human endothelial cell line ECV304 exposed to UV-C, with or without the presence of soybean oil (SBO), was assessed by the Comet assay. After 5-min exposure to UV-C, the %Tail DNA in the ECV304 cells ranged from 0% to 20% for SBO treatment groups and from 50% to 70% for the control group. The result indicated a strong protective effect of SBO against UV-C-induced DNA damage. To clarity the mechanism of this protective effect of SBO, the methanol extract of SBO (MESO) was analyzed and its capacity against UV-C-induced DNA damage was evaluated. Gas chromatography mass spectrometry (GC-MS) analysis confirmed that MESO contained many antioxidants including n-3-polyunsaturated fatty acid (n-3-PUFA), tocopherols and phytosterols. Comet assay revealed that the MESO was also active in reducing the DNA damage dose-dependently (P<0.0001) vs. control in the ECV304 cells. Therefore, we concluded that these potential antioxidants may be responsible for the scavenge of oxidative radicals induced by UV-C irradiation. This study suggested that dietary SBO, which is abundant of antioxidants, may reduce the content or impact of reactive oxygen species (ROS) and lower the risk of diseases caused by ROS.

Vitamin E analog modulates UVB-induced signaling pathway activation and enhances cell survival

We have recently shown that exposure of human keratinocytes to physiologic doses of ultraviolet B (UVB) activates epidermal growth factor receptor (EGFR)/extracellular-regulated kinases 1 and 2 (ERK1/2) and p38 signaling pathways via reactive oxygen species, an effect that can be modulated by antioxidants. Trolox, a water-soluble vitamin E analog, is among the antioxidants that are currently being investigated for their preventive and protective potential against harmful effects of UV radiation to the skin. We found that Trolox inhibits both basal and UVB-induced intracellular H(2)O(2) generation in primary keratinocytes in a concentration-dependent manner. Trolox did not significantly affect UVB-induced phosphorylation of EGFR. Stronger inhibition was observed for ERK1/2 activation at lower, and for p38 activation at higher, concentrations of Trolox added to cells before exposure to UVB. Similarly different effects were found with regard to length of pretreatment with Trolox before UVB exposure-increasing inhibition for ERK1/2 activation at shorter, and for p38 activation at longer, pretreatment intervals. UVB-induced c-jun-N-terminal kinase activation was potently suppressed by Trolox. Also, increasing the pretreatment time of Trolox decreased the rate of cell death following UVB. In conclusion, UVB-induced signaling pathway activation is differentially modulated by Trolox. Further investigation into the time-dependent biologic activation of Trolox and its metabolic products, and modulation of signal transduction with cell outcome should facilitate development of rational strategies for pharmacologic applications.

Diminished blood levels of reduced glutathione and alpha-tocopherol in two triosephosphate isomerase-deficient brothers

The glutathione redox system and alpha-tocopherol, both of which are essential for maintaining the normal structure of biological membranes, some other lipid-soluble antioxidants (lycopene, beta-carotene, retinol), and lipid peroxidation, were investigated in the blood from two triosephosphate isomerase (TPI)-deficient brothers. Both of the genetically identical compound heterozygote brothers have congenital hemolytic anemia, but only one of them has a neurological defect, the second cardinal symptom of TPI deficiency. Whole blood reduced glutathione levels were markedly decreased in both brothers. The glutathione reductase activities as well as the NADPH contents of their erythrocytes were in the normal range or slightly enhanced. Increased ratio of oxidized/reduced glutathione, elevated glutathione S-transferase activity, and increased d-lactate level, a metabolite of the glyoxalase pathway, were detected only in the neurologically affected propositus. The plasma carotenoids (lycopene + beta-carotene), alpha-tocopherol/cholesterol + triglyceride ratios, and the erythrocyte alpha-tocopherol levels were significantly decreased in both patients. It seems conceivable that membrane alterations due to the low level of these reducing agents may contribute to the shortened life span of erythrocytes. The imbalance of the prooxidant/antioxidant homeostasis as well as the increased rate of methylglyoxal formation may also have been involved in the development of the neurological manifestations in the propositus.

dl-alpha-tocopherol, a potent inhibitor of phorbol ester induced shape change of erythro- and megakaryoblastic leukemia cells

Synthetic vitamin E, dl-alpha-tocopherol, added to a human erythroleukemia HEL and a megakaryoblastic leukemia, Meg-01, cell culture produced potent dose-dependent inhibition of phorbol ester-induced adhesion and of the morphologic changes accompanying it. The inhibition was reversible by withdrawal of supplemental vitamin E from the medium. dl-alpha-Tocopherol also inhibited protein kinase C activity both at baseline and after phorbol ester stimulation. Arachidonic acid stimulated protein kinase C activity of erythroleukemia cells and promoted their adhesion, an effect that was also inhibited by dl-alpha-tocopherol. Introduction of a protein kinase C-neutralizing antibody or a protein kinase C-inhibitor substrate into permeabilized HEL cells inhibited phorbol ester-induced adhesion and shape change. dl-alpha-Tocopherol also affected the cellular distribution of protein kinase C, shifting the major portion of the enzyme to the cytosol fraction and reducing phorbol ester-induced membrane association of the enzyme. Thus, protein kinase C appears to mediate shape change and adhesion, both of which are strongly inhibited by dl-alpha-tocopherol.

Cholesterol versus alpha-tocopherol: effects on properties of bilayers made from heteroacid phosphatidylcholines

The techniques of differential scanning calorimetry, fluorescence of merocyanine 540, fluorescence polarization of 1,6-diphenyl-1,3,5-hexatriene, proton permeability, and lipid peroxidation are used to compare the perturbations of cholesterol and alpha-tocopherol on lipid bilayer membranes composed of different phosphatidylcholines containing stearic acid in the sn-1 position and an unsaturated fatty acid (either oleic, alpha-linolenic, gamma-linolenic, or docosahexaenoic acid) in the sn-2 position. It is concluded that the structural roles of cholesterol and alpha-tocopherol may be similar with membranes composed of some phosphatidylcholines but are clearly different with membranes composed of other related phosphatidylcholines. alpha-Tocopherol exerts a much larger effect than cholesterol on membranes rich in polyunsaturated fatty acids that have their initial double bond before the delta 9 position. Cholesterol interacts more favorably with fatty acids that do not have an double bond before the delta 9 position. The membrane structural effects are explained in terms of the larger size of the sterol ring structure of cholesterol compared to the smaller chromanol ring of the alpha-tocopherol.

Actions of arachidonic acid on erythrocyte membrane Rb permeability

The effects of non-esterified arachidonic acid (AA) on erythrocyte membrane ion permeability have been studied using 86Rb flux measurements. [14C]AA was used to quantify membrane incorporation of AA and to show AA removal by albumin washing. The actions of vitamin E and other antioxidants on the effects of AA were examined. Reversible membrane incorporation of 700-2000 nmol AA per ml cells was achieved without significant haemolysis or morphological change. AA incorporation caused a reversible mean increase in bumetanide-sensitive Rb influx of 34% (S.E.M. 4.5, n = 23). This action could be partially prevented by co-incubation with vitamin E, but not by Trolox or dithioerythritol. AA incorporation caused an irreversible mean increase in residual Rb permeability (bumetanide and ouabain insensitive) of 130% (S.E.M. 22, n = 20), associated with a rise in intracellular Na and a fall in intracellular K concentrations. This action was also partially prevented by co-incubation with vitamin E. The effects of AA incorporation on Na,K-ATPase function were difficult to quantify because of the concomitant rises in intracellular Na but the data are consistent with approximately 20% inhibition of activity. Modulation of membrane ion permeability by AA appears to be partially mediated by lipid peroxidation and may have pathophysiological significance.

Vitamin E: more than an antioxidant

The effect of vitamin E on platelet function has been reviewed. Although vitamin E inhibits platelet aggregation in vitro, in vivo it has no significant effect when administered in doses up to 1200 U/day. Platelet adhesion, on the contrary, is strongly inhibited by alpha-tocopherol. Doses of 400 IU/day provide greater than 75% inhibition of platelet adhesion to a variety of adhesive proteins when tested at low shear rate in a laminar flow chamber. The antiadhesive effect of vitamin E appears to be related to a reduction in the number and size of pseudopodia upon platelet activation. This effect of vitamin E may be related to changes in fatty acylation of structural platelet proteins. Clinical studies of vitamin E supplementation in patients with thromboembolic disease are in progress.

Electron spin resonance study of the interaction of alpha-tocopherol with phospholipid model membranes

The effect of up to 20 mol% incorporation of alpha-tocopherol on acyl chain order and dynamics in liquid crystalline phosphatidylcholine (PC) membranes was studied as a function of acyl chain unsaturation by electron spin resonance (ESR) of 5-, 7-, 12- and 16-doxyl spin labelled stearic acids intercalated into the membrane. Order parameters S in the upper portion of the chain (positions 5 and 7) and correlation times tau C in the lower portion (positions 12 and 16) determined from the ESR spectra indicate that in general alpha-tocopherol restricts acyl chain motion within the membrane. The magnitude of the increases in order appears to be dependent upon phospholipid molecular area, being the greatest (up to 15%) in saturated dimyristoylphosphatidylcholine (14:0-14:0 PC) which possesses a relatively small area per molecule as opposed to much smaller increases (less than 3%) in unsaturated PC membranes of larger molecular area. This behavior is interpreted as incompatible with the hypothesis of Lucy and coworkers (A.T. Diplock and J.A. Lucy (1973) FEBS Lett. 29, 205-210), who proposed that membranes are structurally stabilized by interactions between the phytyl side chain of alpha-tocopherol and the polyunsaturated chains of phospholipids.

The effect of vitamin E analogues and long hydrocarbon chain compounds on calcium-induced muscle damage. A novel role for alpha-tocopherol?

Previous studies have demonstrated that supplemental alpha-tocopherol inhibited calcium-induced cytosolic enzyme efflux from normal rat skeletal muscles incubated in vitro and suggested that the protective action was mediated by the phytyl chain of alpha-tocopherol [1]. In order to investigate this further a number of hydrocarbon chain analogues of tocopherol (7,8-dimethyl tocol, 5,7-dimethyl tocol, tocol, alpha-tocotrienol, alpha-tocopherol [10], vitamin K1, vitamin K1 [10], vitamin K1 diacetate, vitamin K2 [20], phytyl ubiquinone and retinol) were tested for any ability to inhibit calcium ionophore, A23187, induced creatine kinase (CK) enzyme efflux. Some compounds were found to be very effective inhibitors and comparison of their structures and ability to inhibit TBARS production in muscle homogenates revealed that the effects did not appear related to antioxidant capacity or chromanol methyl groups, but rather the length and structure of the hydrocarbon chain was the important mediator of the effects seen.

Influence of vitamin E on platelet function in humans

alpha-tocopherol, a natural antioxidant, has been found to inhibit platelet aggregation and release when tested in an in vitro system. This effect of vitamin E was thought to be due to a slight reduction of platelet cyclooxygenase activity and inhibition of lipid peroxide formation. Aggregation of platelets derived from individuals on a dietary supplementation of alpha-tocopherol ranging from 400 to 1200 IU/day showed no significant reduction. The discrepancy between the effectiveness of alpha-tocopherol in vitro and ex vivo is probably related to the levels of alpha-tocopherol attainable in platelets and plasma. Investigation of the effect of alpha-tocopherol on platelet adhesion showed a major inhibitory activity at doses of vitamin E as low as 200 IU/day. Measurements were performed in a laminar flow chamber at both high and low shear rates. Reduced platelet adherence to collagen, fibrinogen, and fibronectin could be documented. alpha-tocopherol-enriched platelets that adhered to adhesive surfaces failed to show the usual long thin pseudopodia but exhibited short, rounded, blunt projections. The reason for this shape change is still unclear, but we speculate that it may be causing the vitamin E-induced reduction of platelet adhesiveness. We believe that dietary supplementation with this vitamin could play a role in the treatment of thromboembolic disease, especially when given in conjunction with an inhibitor of platelet aggregation.

Vitamin E and selenium in gentamicin nephrotoxicity

1. The sequence of renal cellular membrane damage induced by gentamicin was studied in the rat by using the release of alkaline phosphatase, acid phosphatase, muramidase and protein from renal cells as indices of renal damage. 2. The protective effect of a combination of vitamin E and selenium against renal damage was also investigated. 3. Gentamicin (60 mg kg-1 body weight) was nephrotoxic within 12 h of the first dose. 4. The plasma membrane of the renal tubules is damaged before the lysosomal membrane is affected. 5. A combination of vitamin E (1 mg g-1 body weight) and selenium (4 x 10(-3) mg g-1 body weight) attenuates the renal damage induced by gentamicin. Results suggest synergism between vitamin E and selenium in attenuating the renal damage. The possible mechanism of attenuation is discussed. 6. Vitamin E and selenium may have anti-diuretic potential.

Is methyl-branching in alpha-tocopherol's "tail" important for its in vivo activity? Rat curative myopathy bioassay measurements of the vitamin E activity of three 2RS-n-alkyl-2,5,7,8-tetramethyl-6-hydroxychromans

The vitamin E activity of the acetates of three 2RS-n-alkyl-2,5,7,8-tetramethyl-6-hydroxychroman analogs of alpha-tocopherol have been measured and compared directly with all-rac-alpha-tocopheryl acetate, or indirectly via 2R,4'R,8'R-alpha-tocopheryl acetate, using the rat curative myopathy, plasma pyruvate kinase assay. The analogs with alkyl chain lengths of 11 and 13 carbons have activities which not only do not differ significantly (p greater than 0.05) from each other but also do not differ from that of all-rac-alpha-tocopheryl acetate. This finding indicates that methyl branching in the phytyl tail at the 4', 8', and 12' positions has little if any influence upon vitamin E activity. Thus physical interactions involving the methyl branches of the phytyl tail and the polyunsaturated moieties of membrane phospholipids are unimportant in vivo, insofar as this bioassay is concerned. However, the length of the hydrocarbon tail is important. This is indicated by the result obtained with the acetate of the analog with an alkyl chain length of 15 carbon atoms which had only 15% of the activity of 2R,4'R,8'R-alpha-tocopheryl acetate, i.e., 22% of the activity of all-rac-alpha-tocopheryl acetate since this form is 1.47 times less active than 2R,4'R,8'R-alpha-tocopheryl acetate in the curative myopathy bioassay (Weiser, Vecchi, & Schlachter, Internat. J. Vit. Nutr. Res. 55:149-158, 1985).

Modeling cortical cataractogenesis: IX. Activity of vitamin E and esters in preventing cataracts and gamma-crystallin leakage from lenses in diabetic rats

Normal and streptozotocin diabetic female Wistar rats were given vitamin E in the diet as the tocopherol, acetate, or succinate form (2,850 IU/kg food). At the end of 6 weeks, the rats were examined for weight gain or loss, general body condition, and cataracts. At sacrifice, blood was collected for measurement of serum glucose, and gamma-crystallin levels were measured in aqueous and vitreous humors using a radioimmunoassay. One lens was homogenized in 8 M guanidinium chloride for ATP analysis. In normal rats, gamma-crystallin was detected in both aqueous and vitreous humors, with the higher concentration in the vitreous humor. Diabetes caused a sixfold increase in gamma-crystallin in both the aqueous and vitreous humors. Diabetes also led to a significant worsening in general body condition, loss of body weight, formation of cataracts, and decrease in lens ATP levels. Addition of vitamin E and vitamin E succinate, but not vitamin E acetate, to the diet resulted in reduction of gamma-crystallin leakage into the vitreous humors and an increase in body weight. There was no improvement noted for the lens ATP levels, the general body condition, or visual cataract score. Neither streptozotocin-induced diabetes nor vitamin E in the diet appeared to affect the weight of the lenses.

Vitamin E as an in vitro and in vivo antioxidant

alpha-Tocopherol has near optimal activity as a chain-breaking antioxidant. Inherent antioxidant activity plays an important part in determining overall biological activity but the phytyl tail also exerts a very important influence. The new deuterated alpha-tocopherol/GC-MS technique is providing unprecedented insight into the importance of the stereochemistry of the phytyl tail in determining bioavailability, as well as helping to discover how rapidly and effectively absorption, transport, uptake, and loss occur. Measurements of rate of turnover in tissues indicate that differences exist between different types of animals. It is possible that these tissue differences may explain the diverse range of vitamin E deficiency symptoms observed across a wide variety of animals. It is not known what is responsible for the differences in biokinetic behavior.

Model membrane partition ESR study in the presence of alpha-tocopherol by a new spin probe

The effect of alpha-tocopherol (alpha T) on partitioning and fluidity changes occurring in phospholipid liposomes have been investigated by monitoring the X-band ESR spectrum of the high resolution amphiphilic spin probe perdeutero-di-t-butyl nitroxide (PDDTBN), which partitions in the lipid and water phase of liposomes, showing all the three resonances from each phase well resolved.

Physicochemical properties of charge-transfer complexes of plastoquinone and α-tocopherol quinone, and their possible role in vivo

It has been found that the solubility of PQH2 and alpha-TQH2 in hexane increased with the increase in PQ and alpha-TQ concentrations, respectively, that is connected with the formation of quinhydrone-type charge-transfer complexes. Measurements of the solubility of both prenylquinones and their reduced forms in hexane and acetone, at -30 degrees C and room temperature, showed a much higher affinity of the quinol forms for acetone than for hexane. In the case of quinones, the difference in affinity was not significant. The possibility of charge-transfer complex formation by PQ and alpha-TQ in thylakoid membranes and the influence of such complexes on the diffusion of PQH2 and alpha-TQH2 molecules have been considered.

The relationship between alpha-tocopherol and phospholipid fatty acids in rat liver subcellular membrane fractions

(1) A method was devised for the subfractionation of normal rat liver and for the subfractionation of the mitochondrial fraction into inner and outer membrane fractions. The purity of the fractions was assessed using marker enzyme measurements. (2) alpha-Tocopherol was measured in all the fractions by a sensitive HPLC technique. Profiles of phospholipid fatty acids were also determined by gas-liquid chromatography in all the fractions, and these values were calculated in terms of the percentage of each fatty acid in the total fatty acid of the fraction, as well as of the mass of each fatty acid per mumol of phospholipid phosphorus. Tocopherol values were expressed as the mass of tocopherol per g wet liver and per mumol of phospholipid phosphorus. (3) The results show that the mitochondrial and microsomal fractions were the major tocopherol-containing fractions, and both the inner and outer mitochondrial fractions contained substantial amounts of alpha-tocopherol. (4) The mitochondrial and microsomal fractions also had the highest levels of polyunsaturated fatty acids (PUFA) in their phospholipid fraction, especially 20:4 and 22:6, which were particularly localised in the inner mitochondrial membrane fraction. The high inner mitochondrial and microsomal PUFA levels were particularly apparent when the sum of all the unsaturated fatty acids with three or more double bonds was calculated. (5) Calculation of molar ratios of of some phospholipid fatty acids to alpha-tocopherol gave values of the order of several thousand to one. (6) It is concluded that the protective effect of each molecule of alpha-tocopherol must be exerted towards a large number of molecules of membrane unsaturated fatty acids simultaneously. This perhaps implies specific localisation of tocopherol in regions of membrane particularly liable to attack, such as might be expected to occur close to respiratory enzymes that can donate electrons to molecular oxygen.

Reduction of platelet adhesiveness by vitamin E supplementation in humans

Platelet adhesion was tested ex vivo in a group of 7 normal individuals on varying doses of vitamin E. Adhesion to glass slides coated with fibrinogen, fibronectin, collagen I and collagen V was studied by perfusing platelet-rich plasma through a flow chamber. Time- and space-resolved observations of platelet adhesion were made in an area of parallel flow lines and low shear rate under standardized conditions before and after dietary supplementation with vitamin E. The doses varied from 400 I.U./day to 1600 I.U./day in 400 I.U. increments. A statistically significant reduction in platelet adhesion was noted on all four adhesive surfaces at the 400 I.U. level of vitamin E supplementation. This reduction varied in magnitude depending on the adhesive surface. As vitamin E supplementation was increased, no dose-dependent downward trend in adhesion rate was observed although the platelet alpha-tocopherol content progressively increased. Based on our results, we suggest that 400 I.U./day may be a near optimal dose of vitamin E to reduce platelet adhesivity as evaluated in our flow chamber system.

Liposomes as membrane model for study of lipid peroxidation

This article describes the properties, production and characterization of liposomes with special reference to their use as membrane model for the study of lipid peroxidation. It presents briefly the methods that can be used for the assay of liposomal lipid peroxidation and brings out the special advantages these liposomes provide in elucidating the mechanism of lipid peroxidation by different physical and chemical agents. Studies involving liposomal lipid peroxidation by different agents and the consequent changes in the structure and function of liposomal membrane have been reviewed briefly.

Effect of tocopherol and taurine on membrane fluidity of retinal rod outer segments

The deficiency of taurine and alpha-tocopherol results in disturbances of the structure of retinal rod outer segments. In this study the effect of alpha-tocopherol (vitamin E) and taurine on the fluidity of membranes from frog retinal rod outer segments and of liposomes prepared with lecithin or with lipids from outer segment membranes was examined by steady-state fluorescence polarization of diphenyl-hexatriene (DPH). alpha-Tocopherol increased the DPH anisotropy parameter in both preparations. The vitamin modified the breakpoint temperature of Arrhenius plots of DPH anisotropy, and decreased the activation energy. Taurine failed to modify any of the parameters examined in both outer segment membranes and lecithin liposomes. These results suggest a stabilizer role for tocopherol in rod outer segment membranes. In contrast, the requirement of taurine to maintain outer segment structure seems unrelated to an effect on the physical state of membrane lipids.

Toxicity of ozone and nitrogen dioxide to alveolar macrophages: comparative study revealing differences in their mechanism of toxic action

The toxicity of ozone and nitrogen dioxide is generally ascribed to their oxidative potential. In this study their toxic mechanism of action was compared using an intact cell model. Rat alveolar macrophages were exposed by means of gas diffusion through a Teflon film. In this in vitro system, ozone appeared to be 10 times more toxic than nitrogen dioxide. alpha-Tocopherol protected equally well against ozone and nitrogen dioxide. It was demonstrated that alpha-tocopherol provided its protection by its action as a radical scavenger and not by its stabilizing structural membrane effect, as (1) concentrations of alpha-tocopherol that already provided optimal protection against ozone and nitrogen dioxide did not influence the membrane fluidity of alveolar macrophages and (2) neither one of the structural alpha-tocopherol analogs tested (phytol and the methyl ether of alpha-tocopherol) could provide a protection against ozone or nitrogen dioxide comparable to the one provided by alpha-tocopherol. It was concluded that reactive intermediates scavenged by alpha-tocopherol are important in the toxic mechanism of both ozone and nitrogen dioxide induced cell damage. However, further results presented strongly confirmed that the kind of radicals and/or reactive intermediates, and thus the toxic reaction mechanism involved, must be different in ozone- and nitrogen dioxide-induced cell damage. This was concluded from the observations that showed that (1) vitamin C provided significantly better protection against nitrogen dioxide than against an equally toxic dose of ozone, (2) glutathione depletion affected the cellular sensitivity toward ozone to a significantly greater extent than the sensitivity towards nitrogen dioxide, and (3) the scavenging action of alpha-tocopherol was accompanied by a significantly greater reduction in its cellular level during nitrogen dioxide exposure than during exposure to ozone. One of the possibilities compatible with the results presented in this study might be that lipid (peroxyl) free radicals formed in a radical-mediated peroxidative pathway, resulting in a substantial breakdown of cellular alpha-tocopherol, are involved in nitrogen dioxide-induced cell damage, and that lipid ozonides, scavenged by alpha-tocopherol as well, are involved in ozone-induced cell damage.

Vitamin E in young and old human red blood cells

Young and old human red blood cells contain about the same amount of alpha-tocopherol, a compound which has previously been shown to be the major lipid-soluble, chain-breaking antioxidant present in such cells. Since red blood cells lose up to ca. 20% of lipid material from their membrane as they age, the alpha-tocopherol/membrane-lipid ratio actually rises with age rather than declining as might have been expected on the basis of the free radical theory of aging. The alpha-tocopherol/arachidonic acid moiety ratios increase in the order: young red blood cells less than old red blood cells less than plasma, which argues against the suggested membrane stabilizing effect of alpha-tocopherol/arachidonic acid moiety complexes.

Effects of alpha-tocopherol on the lipid peroxidation and fluidity of porcine intestinal brush-border membranes

The effect of alpha-tocopherol on the lipid fluidity of porcine intestinal brush-border membranes was studied using pyrene as a fluorescent probe. Addition of alpha-tocopherol to the medium decreased fluorescence intensity and lifetime, but increased the fluorescence polarization of pyrene-labeled membranes. beta-, gamma-, and delta-Tocopherols gave no appreciable effect on the fluorescence intensity and polarization of the complex. The apparent dissociation constant (3.1 +/- 0.12 microM) of the interaction of alpha-tocopherol with the membranes, estimated from the change in the fluorescence intensity with varying concentrations of alpha-tocopherol, was in good agreement with the concentration required to cause the half-maximal inhibition of lipid peroxidation of the membranes performed by incubation with 100 microM ascorbic acid and 10 microM Fe2+. Decrease of the slope in the thermal Perrin plot of the polarization of pyrene-labeled membranes by alpha-tocopherol suggests that the movement of pyrene molecules in the membranes is restricted by binding of the tocopherol. This interpretation was confirmed by an increased harmonic mean of the rotational relaxation time of the dye molecules in the membranes from 10.9 +/- 0.16 to 18.5 +/- 0.51 microseconds after addition of 25 microM alpha-tocopherol to the medium. The perturbation of lipid phase in the membranes induced by alpha-tocopherol was also suggested from a decreased quenching rate constant of pyrene fluorescence in the membranes for Tl+. Based on these results, the effect of alpha-tocopherol on the lipid fluidity of the membranes is discussed.

Proton magnetic resonance spectroscopic studies of the interaction of ubiquinone-10 with phospholipid model membranes

Proton magnetic resonance spectra of ubiquinone-10 and ubiquinone-10 dispersed with dipalmitoylglycerophosphocholine or egg phosphatidylcholine in aqueous medium have been obtained. The dispersions are in the form of multilamellar liposomes as judged by 31P-NMR spectra and the thermal history of the samples have ensured that ubiquinone not incorporated into the phospholipid structure only gives rise to a broad-line NMR proton spectrum. A high-resolution proton spectrum of ubiquinone is observed with upfield shifts of the O-methyl protons of the benzoquinone rings, indicating close proximity of the molecules but with an arrangement different from the pure liquid ubiquinone. Spectra obtained in the presence of the lanthanide shift reagents, dysprosium fluorooctanedionate and Dy(NO3)3, which have a preferred location in the hydrophobic and hydrophilic domains, respectively, of ubiquinone/phospholipid codispersions, are consistent with the partitioning of ubiquinone into a hydrophobic phospholipid environment remote from the aqueous phase. The type of arrangements of ubiquinone that could be accommodated within bilayers of phospholipid are discussed.