Phospholipid transfer protein deficiency protects circulating lipoproteins from oxidation due to the enhanced accumulation of vitamin E

Vitamin E is a lipophilic anti-oxidant that can prevent the oxidative damage of atherogenic lipoproteins. However, human trials with vitamin E have been disappointing, perhaps related to ineffective levels of vitamin E in atherogenic apoB-containing lipoproteins. Phospholipid transfer protein (PLTP) promotes vitamin E removal from atherogenic lipoproteins in vitro, and PLTP deficiency has recently been recognized as an anti-atherogenic state. To determine whether PLTP regulates lipoprotein vitamin E content in vivo, we measured alpha-tocopherol content and oxidation parameters of lipoproteins from PLTP-deficient mice in wild type, apoE-deficient, low density lipoprotein (LDL) receptor-deficient, or apoB/cholesteryl ester transfer protein transgenic backgrounds. In all four backgrounds, the vitamin E content of very low density lipoprotein (VLDL) and/or LDL was significantly increased in PLTP-deficient mice, compared with controls with normal plasma PLTP activity. Moreover, PLTP deficiency produced a dramatic delay in generation of conjugated dienes in oxidized apoB-containing lipoproteins as well as markedly lower titers of plasma IgG autoantibodies to oxidized LDL. The addition of purified PLTP to deficient plasma lowered the vitamin E content of VLDL plus LDL and normalized the generation of conjugated dienes. The data show that PLTP regulates the bioavailability of vitamin E in atherogenic lipoproteins and suggest a novel strategy for achieving more effective concentrations of anti-oxidants in lipoproteins, independent of dietary supplementation.     

Coenzyme Q10: Absorption,Antioxidative Properties,Determinants, and Plasma Levels

The purpose of this article is to summarise our studies, in which the main determinants and absorption of plasma coenzyme Q10 (Q10, ubiquinone) have been assessed, and the effects of moderate dose oral Q10 supplementation on plasma antioxidative capacity, lipoprotein oxidation resistance and on plasma lipid peroxidation investigated. All the supplementation trials carried out have been blinded and placebo-controlled clinical studies. Of the determinants of Q10, serum cholesterol, serum triglycerides, male gender, alcohol consumption and age were found to be associated positively with plasma Q10 concentration. A single dose of 30 mg of Q10, which is the maximum daily dose recommended by Q10 producers, had only a marginal elevating effect on plasma Q10 levels in non-Q10-deficient subjects. Following supplementation, a dose-dependent increase in plasma Q10 levels was observed up to a daily dose of 200 mg, which resulted in a 6.1-fold increase in plasma Q10 levels. However, simultaneous supplementation with vitamin E resulted in lower plasma Q10 levels. Of the lipid peroxidation measurements, Q10 supplementation did not increase LDL TRAP, plasma TRAP, VLDL+LDL oxidation resistance nor did it decrease LDL oxidation susceptibility ex vivo. Q10 with minor vitamin E dose neither decreased exercise-induced lipid peroxidation ex vivo nor muscular damage. Q10 supplementation might, however, decrease plasma lipid peroxidation in vivo, as assessed by the increased proportion of plasma ubiquinol (reduced form, Q10H 2 ) of total Q10. High dose vitamin E supplementation decreased this proportion, which suggests in vivo regeneration of tocopheryl radicals by ubiquinol.     

Coenzyme Q10: absorption, antioxidative properties, determinants, and plasma levels

The purpose of this article is to summarise our studies, in which the main determinants and absorption of plasma coenzyme Q10 (Q10, ubiquinone) have been assessed, and the effects of moderate dose oral Q10 supplementation on plasma antioxidative capacity, lipoprotein oxidation resistance and on plasma lipid peroxidation investigated. All the supplementation trials carried out have been blinded and placebo-controlled clinical studies. Of the determinants of Q10, serum cholesterol, serum triglycerides, male gender, alcohol consumption and age were found to be associated positively with plasma Q10 concentration. A single dose of 30 mg of Q10, which is the maximum daily dose recommended by Q10 producers, had only a marginal elevating effect on plasma Q10 levels in non-Q10-deficient subjects. Following supplementation, a dose-dependent increase in plasma Q10 levels was observed up to a daily dose of 200 mg, which resulted in a 6.1-fold increase in plasma Q10 levels. However, simultaneous supplementation with vitamin E resulted in lower plasma Q10 levels. Of the lipid peroxidation measurements, Q10 supplementation did not increase LDL TRAP, plasma TRAP, VLDL+LDL oxidation resistance nor did it decrease LDL oxidation susceptibility ex vivo. Q10 with minor vitamin E dose neither decreased exercise-induced lipid peroxidation ex vivo nor muscular damage. Q10 supplementation might, however, decrease plasma lipid peroxidation in vivo , as assessed by the increased proportion of plasma ubiquinol (reduced form, Q10H 2 ) of total Q10. High dose vitamin E supplementation decreased this proportion, which suggests in vivo regeneration of tocopheryl radicals by ubiquinol.     

Effect of genistein supplementation on tissue genistein and lipid peroxidation of serum, liver and low-density lipoprotein in hamsters

The aim of this study was to investigate the effects of genistein supplementation in a vitamin E-deficient diet on the genistein concentrations and the lipid oxidation of serum, liver and low-density lipoprotein (LDL) of hamsters. Thirty-six male hamsters were randomly divided into three groups and fed a vitamin E-deficient semisynthetic diet (AIN-76) containing different levels of genistein, i.e., G0 (control group, genistein-free diet), G50 (50 mg genistein/kg diet) and G200 (200 mg genistein/kg diet) for 5 weeks. The concentrations of genistein in serum and liver significantly increased with the increase of genistein supplementation. The vitamin E contents in LDL were higher in hamsters fed G50 or G200 diets than in hamsters fed genistein-free diet. Genistein supplementation to hamsters significantly reduced the propagation rate during conjugated diene formation of LDL oxidation, and the lag time of LDL oxidation in hamsters fed G200 diets was significantly lower than that of G0 diets. In addition, genistein supplementation significantly raised serum total antioxidant capacity and decreased the thiobarbituric acid-reactive substances (TBARS) of LDL and liver in hamsters. However, no significant differences in TBARS were found in serum, irrespective of genistein addition. On the other hand, the relative contents of polyunsaturated fatty acids in LDL were decreased after genistein supplementation. There was a negative correlation between lag time and P/S ratio, and a positive correlation between lag time and vitamin E contents. These data demonstrate that genistein supplementation markedly increased its concentrations in body tissues and reduced oxidative stress of lipid oxidation of serum, liver and LDL.     

Oxidation of low-density lipoprotein in atherosclerosis from basic biochemistry to clinical studies

Although it has been known for long time that atherosclerosis is associated with lipid deposition, only recently it has been accepted that the plasmatic concentration of cholesterol, especially LDL cholesterol, is a risk factor for atherosclerosis. However, chemically modified LDL, but not native LDL, is able to induce the formation of foam cells, the hallmark of atherosclerosis. LDL oxidation is likely to be the most important form of LDL modification in humans. In biochemical terms, LDL oxidation is a free radical driven chain reaction where polyunsaturated fatty acids are converted to lipid peroxides, which easily decompose to many products, including biologically active aldehydes. The assay of LDL oxidation in biological fluids is problematic; direct assays detect a product of LDL oxidation whereas indirect assays give an indicator of LDL oxidation susceptibility. In general, epidemiological studies support the concept that the level of plasmatic lipophilic antioxidants, tocopherols and carotenoids, is low in populations at increased risk for atherosclerosis. However, clinical trials based on vitamin E as antioxidant showed inconclusive results, suggesting that supplementation with vitamin E is not generically recommended for atherosclerotic patients. These results, however, do not contradict that oxidation of lipoprotein is involved in atherosclerosis; rather, this negative outcome raises a number of considerations such as the need for a reliable marker of lipoprotein oxidation in plasma and a more complete information about the physiological triggers of lipoprotein oxidation.     

A role for reduced coenzyme Q in atherosclerosis?

Substantial evidence implicates oxidative modification of low density lipoprotein (LDL) as an important event contributing to atherogenesis. As a result, the elucidation of the molecular mechanisms by which LDL is oxidized and how such oxidation is prevented by antioxidants has been a significant research focus. Studies on the antioxidation of LDL lipids have focused primarily on alpha-tocopherol (alpha-TOH), biologically and chemically the most active form of vitamin E and quantitatively the major lipid-soluble antioxidant in extracts prepared from human LDL. In addition to alpha-TOH, plasma LDL also contains low levels of ubiquinol-10 (CoQ10H2; the reduced form of coenzyme Q10). Recent studies have shown that in oxidizing plasma lipoproteins alpha-TOH can exhibit anti- or pro-oxidant activities for the lipoprotein's lipids exposed to a vast array of oxidants. This article reviews the molecular action of alpha-TOH in LDL undergoing "mild" radical-initiated lipid peroxidation, and discusses how small levels of CoQ10H2 can represent an efficient antioxidant defence for lipoprotein lipids. We also comment on the levels alpha-TOH, CoQ10H2 and lipid oxidation products in the intima of patients with coronary artery disease and report on preliminary studies examining the effect of coenzyme Q10 supplementation on atherogenesis in apolipoprotein E knockout mice.     

Tocopherol-mediated peroxidation of lipoproteins: implications for vitamin E as a potential antiatherogenic supplement.

The 'oxidation theory' of atherosclerosis proposes that oxidation of low density lipoprotein (LDL) contributes to atherogenesis. Although little direct evidence for a causative role of 'oxidized LDL' in atherogenesis exists, several studies show that, in vitro, oxidized LDL exhibits potentially proatherogenic activities and lipoproteins isolated from atherosclerotic lesions are oxidized. As a consequence, the molecular mechanisms of LDL oxidation and the actions of alpha-tocopherol (alpha-TOH, vitamin E), the major lipid-soluble lipoprotein antioxidant, have been studied in detail. Based on the known antioxidant action of alpha-TOH and epidemiological evidence, vitamin E is generally considered to be beneficial in coronary artery disease. However, intervention studies overall show a null effect of vitamin E on atherosclerosis. This confounding outcome can be rationalized by the recently discovered diverse role for alpha-TOH in lipoprotein oxidation; that is, alpha-TOH displays neutral, anti-, or, indeed, pro-oxidant activity under various conditions. This review describes the latter, novel action of alpha-TOH, termed tocopherol-mediated peroxidation, and discusses the benefits of vitamin E supplementation alone or together with other antioxidants that work in concert with alpha-TOH in ameliorating lipoprotein lipid peroxidation in the artery wall and, hence, atherosclerosis.     

Effect of dietary supplementation with alpha-tocopherol on the oxidative modification of low density lipoprotein.

Much data has accumulated supporting a proatherogenic role for oxidized low density lipoprotein (Ox-LDL). Micronutrient antioxidants such as alpha-tocopherol, the principal lipid-soluble antioxidant, assume potential significance because levels can be manipulated by dietary measures without resulting in side effects. Co-incubation of LDL in vitro with alpha-tocopherol inhibits its oxidative modification. Hence the effect of dietary supplementation with alpha-tocopherol on the time course of copper-catalyzed oxidation of LDL was tested in a randomized placebo-controlled single-blind study. Two groups of 12 male subjects were given either placebo or alpha-tocopherol (800 IU/day) for a period of 12 weeks. Alpha-tocopherol therapy did not result in any side effects or exert an adverse effect on the plasma lipid and lipoprotein profile. While the lipid standardized alpha-tocopherol levels were similar at baseline, the supplemented group had 3.3-fold and 4.4-fold higher levels compared to placebo at 6 and 12 weeks, respectively. In the 15 subjects in whom both plasma and LDL alpha-tocopherol levels were quantitated, there was a significant correlation (r = 0.79, P less than 0.0001). At baseline there were no significant differences in the time course curves of thiobarbituric acid-reacting substances (TBARS) activity or conjugated diene formation between the alpha-tocopherol and placebo groups. However, at both 6 and 12 weeks the mean levels of TBARS activity and conjugated diene formation were lower in the alpha-tocopherol group; the most significant differences were manifest at the 3-h time point. Also at both 6 and 12 weeks the mean rate of oxidation was lower in the alpha-tocopherol group.2+_     

Protection of low density lipoprotein oxidation by the antioxidant agent IRFI005, a new synthetic hydrophilic vitamin E analogue

The oxidative modification of low density lipoprotein (LDL) is thought to be an important factor in the initiation and development of atherosclerosis. Antioxidants have been shown to protect LDL from oxidation and to inhibit atherosclerosis development in animals. Potent synthetic antioxidants are currently being tested, but they are not necessarily safe for human use. We here characterize the antioxidant activity of IRFI005, the active metabolite of Raxofelast (IRFI0016) that is a novel synthetic analog of vitamin E under clinical development, and demonstrate that it prevents oxidative modification of LDL. IFI005 inhibited the oxidative modification of LDL, measured through the generation of MDA, electrophoretic mobility and apo B100 fluorescence. During the oxidation process IRF1005 was consumed with the formation of the benzoquinone oxidation product. The powerful antioxidant activity of IRFI005 is at least in part mediated by a chain breaking mechanism as it is an efficient peroxyl radical scavenger with a rate constant k(IRFI005 + LOO(o)) of 1.8 X 10(6) M(-1)s(-1). 4. IRFI005 substantially preserved LDL-associated antioxidants, alpha-tocopherol and carotenoids, and when co-incubated with physiologic levels of ascorbate provoked a synergistic inhibition of LDL oxidation. Also the co-incubation of IRFI005 with Trolox caused a synergistic effect, and a lag phase in the formation of the trolox-benzoquinone oxidation product. A synergistic inhibition of lipid peroxidation was also demonstrated by co-incubating IRFI005 and alpha-tocopherol incorporated in linoleic acid micelles. These data strongly suggest that IRFI005 can operate by a recycling mechanism similar to the vitamin E/ascorbate sysem.     

Age-related decrease of dehydroepiandrosterone concentrations in low density lipoproteins and its role in the susceptibility of low density lipoproteins to lipid peroxidation

The incidence of atherosclerosis and related diseases increases with age. The aging process may enhance lipoprotein modification, which leads to an increase in the susceptibility of low density lipoprotein (LDL) and high density lipoprotein (HDL) to oxidation. Dehydroepiandrosterone (DHEA), the most abundant steroid hormone in humans, has been shown to have antiatherogenic effects. This hormone also decreases dramatically with age. In the present study, we were interested in determining the presence of DHEA/DHEAS (dehydroepiandrosterone sulfate) and changes in their concentrations in HDL and LDL lipoproteins with age. Moreover, we studied the susceptibility of LDL to oxidation with age in the presence or absence of vitamin E or DHEA. We demonstrated that vitamin E is unable to restore the decreased resistance to oxidation of LDL from elderly subjects to that of LDL obtained from young subjects. Furthermore, our results provide evidence that DHEA is an integral part of LDL and HDL and disappears to almost nondetectable levels during aging. The DHEA incorporated into the LDL from elderly subjects increased LDL resistance to oxidation in a concentration-dependent manner. The increased resistance provided by DHEA was higher than that with vitamin E. DHEA seems to act either by protecting vitamin E from disappearance from LDL under oxidation or by scavenging directly the free radicals produced during the oxidative process. Our results suggests that DHEA exerts an antioxidative effect on LDL, which could have antiatherogenic consequences. Careful clinical trials of DHEA replacement should determine whether this ex vivo effect could be translated into any measurable antiatherogenic (cardioprotective) action.     

Serum ex vivo lipoprotein oxidizability in patients with ischemic heart disease supplemented with vitamin E

The decreased oxidizability of plasma lipoproteins is related to the increased vitamin E intake and its association with a relatively lower incidence of coronary heart disease has been proposed. We investigated the effect of the in vivo vitamin E supplementation on the oxidizability of serum lipids in patients with ischemic heart disease and a moderate hypercholesterolemia. Thirty-two patients (16 males and 16 postmenopausal women) participated in this placebo-controlled, randomized trial. They were treated with 400 mg vitamin E/day for 6 weeks. The copper-induced serum lipid oxidizability ex vivo was assessed by measuring conjugated diene formation at 245 nm. We also measured vitamin E, malondialdehyde (MDA) and uric acid concentrations in the plasma. Because of observed significant differences in parameters of serum lipid oxidizability (lag time and maximal rate of oxidation), plasma alpha-tocopherol and MDA levels between male patients and postmenopausal women supplemented with vitamin E, the results were compared between both genders. Six weeks of vitamin E supplementation significantly increased plasma vitamin E levels (by 87 %) in male patients but in postmenopausal women only by 34 %. Concomitantly with increased plasma levels of vitamin E the decrease in plasma MDA levels was observed in male patients (decrease by 20 %; p=0.008), but in postmenopausal women the decrease did not attain statistical significance. Plasma uric acid levels were not apparently changed in placebo or vitamin E supplemented groups of patients. The changes in ex vivo serum lipid oxidizability after vitamin E, supplementation have shown a significantly prolonged lag time (by 11 %; p=0.048) and lowered rate of lipid oxidation (by 21 %; p=0.004) in male patients in comparison with postmenopausal women. Linear regression analysis revealed a significant correlation between plasma vitamin E levels and the lag time (r=0.77; p=0.03) and the maximal rate of serum lipid oxidation (r=-0.70; p=0.05) in male patients. However, in postmenopausal women the correlations were not significant. We conclude that 400 mg vitamin E/day supplementation in patients with ischemic heart disease and a moderate hypercholesterolemia influenced favorably ex vivo serum lipid oxidation of male patients when compared with postmenopausal women. The observed differences between both genders could be useful in the selection of the effective vitamin E doses in the prevention of coronary heart disease.     

Oral alpha-tocopherol supplementation inhibits lipid oxidation in established human atherosclerotic lesions

BACKGROUND: Much experimental evidence suggests that lipid oxidation is important in atherogenesis and in epidemiological studies dietary antioxidants appear protective against cardiovascular events. However, most large clinical trials failed to demonstrate benefit of oral antioxidant vitamin supplementation in high-risk subjects. This paradox questions whether ingestion of antioxidant vitamins significantly affects lipid oxidation within established atherosclerotic lesions. METHODS AND RESULTS: This placebo-controlled, double blind study of 104 carotid endarterectomy patients determined the effects of short-term alpha-tocopherol supplementation (500 IU/day) on lipid oxidation in plasma and advanced atherosclerotic lesions. In the 53 patients who received alpha-tocopherol there was a significant increase in plasma alpha-tocopherol concentrations (from 32.66 +/- 13.11 at baseline to 38.31 +/- 13.87 (mean +/- SD) micromol/l, p < 0.01), a 40% increase (compared with placebo patients) in circulating LDL-associated alpha-tocopherol (p < 0.0001), and their LDL was less susceptible to ex vivo oxidation than that of the placebo group (lag phase 115.3 +/- 28.2 and 104.4 +/- 15.7 min respectively, p < 0.02). Although the mean cholesterol-standardised alpha-tocopherol concentration within lesions did not increase, alpha-tocopherol concentrations in lesions correlated significantly with those in plasma, suggesting that plasma alpha-tocopherol levels can influence lesion levels. There was a significant inverse correlation in lesions between cholesterol-standardised levels of alpha-tocopherol and 7beta-hydroxycholesterol, a free radical oxidation product of cholesterol. CONCLUSIONS: These results suggest that within plasma and lesions alpha-tocopherol can act as an antioxidant. They may also explain why studies using < 500 IU alpha-tocopherol/day failed to demonstrate benefit of antioxidant therapy. Better understanding of the pharmacodynamics of oral antioxidants is required to guide future clinical trials.     

Effects of exogenous vitamin E supplementation on the levels of oxidants and antioxidants in chronic obstructive pulmonary disease

Oxidative stress has been recognized as a central feature of smoke induced chronic obstructive pulmonary disease (COPD). Imbalance between oxidant and antioxidant enzymes is also an established fact in these patients. But studies in regard to stable COPD patients and effect of vitamin E supplementation are lacking. Thirty patients with COPD were included in the study. Their baseline clinical examination, spirometry, plasma malondialdehyde (MDA), alpha-tocopherol and red blood cell superoxide dismutase (SOD) levels were mea sured. Twenty healthy non-smokers who were matched for age and sex served as controls. All the above parameters were repeated after 12 weeks of supplementation with 400 IU of vitamin E daily. The mean malondialdehyde levels in the patients at baseline were higher than controls (5.91 +/- 1.23 nmol/ml vs 4.55 +/- 1.51 nmol/ml, P = 0 001), so also was plasma alpha-tocopherol levels (P < 0 001), while SOD levels were lower in the patients compared to controls (1692 +/- 259 units g/Hb vs 2451 +/- 131 units g/Hb, P < 0 001). Exogenous vitamin E (400 IU per day) supplementation did not bring about any significant change in plasma alpha-tocopherol and SOD levels. The Pearson s co-efficient of correlation between the levels of MDA, vitamin E, SOD; and spirometric measurements were not significant either on day 1 or after 12 weeks of vitamin E supplementation. The present study shows that initially the plasma lipid peroxide (MDA) levels are high and antioxidants (alpha-tocopherol and SOD) are low in patients with COPD. Exogenous supplementation with vitamin E does not have any significant effect on the spirometric measurements though it brings down the levels of MDA showing attenuation of further damage. However, inclusion of larger number of patients and supple mentation with vitamin E for longer periods may throw more light on free radical injury and protective effects of antioxidants.     

Alpha-tocopherol supplementation does not affect monocyte endothelial adhesion or C-reactive protein levels but reduces soluble vascular adhesion molecule-1 in the plasma of healthy subjects

Vascular monocyte retention in the subintima is pivotal to the development of cardiovascular disease and is facilitated by up-regulation of adhesion molecules on monocytes/endothelial cells during oxidative stress. Epidemiological studies have shown that cardiovascular disease risk is inversely proportional to plasma levels of the dietary micronutrients, vitamin C and vitamin E (alpha-tocopherol). We have tested the hypothesis that alpha-tocopherol supplementation may alter endothelial/monocyte function and interaction in subjects with normal ascorbate levels (> 50 microM), as ascorbate has been shown to regenerate tocopherol from its oxidised tocopheroxyl radical form in vitro. Healthy male subjects received alpha-tocopherol supplements (400 IU RRR-alpha-tocopherol/day for 6 weeks) in a placebo-controlled, double-blind intervention study. There were no significant differences in monocyte CD11b expression, monocyte adhesion to endothelial cells, plasma C-reactive protein or sICAM-1 concentrations post-supplementation. There was no evidence for nuclear translocation of NF-kappaB in isolated resting monocytes, nor any effect of alpha-tocopherol supplementation. However, post-supplementation, sVCAM-1 levels were decreased in all subjects and sE-selectin levels were increased in the vitamin C-replete group only; a weak positive correlation was observed between sE-selectin and alpha-tocopherol concentration. In conclusion, alpha-tocopherol supplementation had little effect on cardiovascular disease risk factors in healthy subjects and the effects of tocopherol were not consistently affected by plasma vitamin C concentration.     

Autoantibody against oxidized low-density lipoproteins may be enhanced by cigarette smoking

A total of 59 healthy male subjects (32 smokers and 27 nonsmokers) who had no reported systemic disease and did not take alcohol and vitamin supplementation were included. The levels of autoantibody to oxidized low-density lipoproteins (ox-LDL) in smokers and age-matched nonsmokers were compared. The plasma levels of antioxidants that can affect the formation of ox-LDL were also measured, and correlation analyses between anti ox-LDL IgG and plasma antioxidants, controlling for age and body mass index (BMI), were performed. Plasma alpha-tocopherol and uric acid concentrations of nonsmokers (2.78+/-1.09 microg/mg total lipid and 6.96+/-1.69 mg/dl, respectively) were significantly higher than those of smokers (1.68+/-0.48 microg/mg total lipid and 6.15+/-1.14 mg/dl, respectively) (P<0.05). Although plasma ascorbate and retinol levels were not significantly different between smokers and nonsmokers, smokers older than 45 years old had significantly lower plasma ascorbate levels (0.32+/-0.17 mg/dl) than age-matched nonsmokers (0. 53+/-0.14 mg/dl) (P=0.036). Higher level of plasma anti ox-LDL IgG was noted in the group of smokers compared with nonsmokers (515+/-409 mU/ml vs. 407+/-268 mU/ml, respectively) under the statistic method of Chi-Square test (P=0.049). A significant negative correlation was found between plasma anti ox-LDL IgG and alpha-tocopherol in the combined population as well as in the smoker group (r=-0.26, p=0.047; r=-0.48, p=0.006; respectively). However, there was no correlation between plasma anti ox-LDL IgG and the levels of other antioxidants. These results suggest that reduced concentrations of alpha-tocopherol are associated with cigarette smoking. The significantly negative correlation between plasma anti ox-LDL IgG and alpha-tocopherol in the entire study population as well as in the smoker group suggests that plasma alpha-tocopherol may be partially effective if not totally at protecting LDL from oxidative damage caused by cigarette smoking and dietary supplementation with alpha-tocopherol may provide a protective effect against LDL oxidation, especially in smokers.     

The monoterpene terpinolene from the oil of Pinus mugo L. in concert with alpha-tocopherol and beta-carotene effectively prevents oxidation of LDL.

Antioxidants from several nutrients, e.g. vitamin E, beta-carotene, or flavonoids, inhibit the oxidative modification of low-density lipoproteins. This protective effect could possibly retard atherogenesis and in consequence avoid coronary heart diseases. Some studies have shown a positive effect of those antioxidants on cardiovascular disease. Another class of naturally occurring antioxidants are terpenoids, which are found in essential oils. The essential oil of Pinus mugo and the contained monoterpene terpinolene effectively prevent low-density lipoprotein (LDL)-oxidation. In order to test the mechanism by which terpinolene protects LDL from oxidation, LDL from human blood plasma enriched in terpinolene was isolated. In this preparation not only the lipid part of LDL is protected against copper-induced oxidation--as proven by following the formation of conjugated dienes, but also the oxidation of the protein part is inhibited, since loss of tryptophan fluorescence is strongly delayed. This inhibition is due to a retarded oxidation of intrinsic carotenoids of LDL, and not, as in the case of some flavonoids, attributable to a protection of intrinsic alpha-tocopherol. These results are in agreement with our previous results, which showed the same effects for a monoterpene from lemon oil, i.e. gamma-terpinene.     

Effect of vitamin E on aortic lipid oxidation and intimal proliferation after arterial injury in cholesterol-fed rabbits.

Oxidized low-density lipoproteins (LDL) are implicated in atherosclerosis. However, large-scale intervention studies designed to test whether antioxidants, such as vitamin E, can ameliorate cardiovascular disease have generated ambivalent results. This may relate to the fact that the mechanism whereby lipid oxidation is initiated in vivo is unknown and the lack of direct evidence for a deficiency of antioxidants in atherosclerotic lesions. Further, there is little evidence to suggest that vitamin E acts as an antioxidant for lipid peroxidation in vivo. Here we tested the antioxidant effect of dietary vitamin E (alpha-tocopherol) supplementation on intimal proliferation and lipid oxidation in balloon-injured, hypercholesterolemic rabbits. alpha-Tocopherol supplementation increased vascular content of alpha-tocopherol over 30-fold compared to nonsupplemented and alpha-tocopherol-deficient chows. Balloon injury resulted in oxidized lipid deposition in the aorta. Maximum levels of primary lipid oxidation products, measured as hydroperoxides of esterified lipid (LOOH) and oxidized linoleate (HODE), were 0.22 and 1.10 nmol/mg, representing 0.21 and 0.39% of the precursor molecule, respectively. Secondary lipid oxidation products, measured as oxysterols, were maximal at 5.60 nmol/mg or 1.48% of the precursor compound. Vascular HODE and oxysterols were significantly reduced by vitamin E supplementation. However, the intima/media ratio of aortic vessels increased with vitamin E supplementation, suggesting that the antioxidant promoted intimal proliferation. Thus, the study demonstrates a dissociation of aortic lipid oxidation and lesion development, and suggests that vitamin E does not prevent lesion development in this animal model.     

Smoking has no effect on the amino acid composition of apolipoprotein B100 of LDL while directly influencing the antioxidant status

Previous studies have demonstrated increased plasma levels of oxidised low-density lipoprotein (oxLDL) in chronic smokers, which has been associated with the extent of endothelial dysfunction. In this study we examine the relationship between the amino acid composition of apolipoprotein B100 (apo B) of low-density lipoprotein (LDL), by reverse phase HPLC after precolumn derivatisation, between smokers (> or =40 cigarettes/day) and nonsmokers in relation to their plasma and LDL antioxidant status. While there was a significant difference in the levels of plasma vitamin C and alpha-tocopherol between female smokers and nonsmokers, as well as in the levels of LDL alpha-tocopherol, there was no significant difference in the amino acid composition of apo B between the two groups.     

Increased Resistance to Oxidation of Betalain-enriched Human Low Density Lipoproteins

Betalains are natural pigments recently considered as compounds with potential antioxidative properties. In this work, ex vivo plasma spiking of pure either betanin or indicaxanthin, followed by isolation of low density lipoprotein (LDL), and measurement of its resistance to copper-induced oxidation, has been used to research if these betalains can bind to LDL and prevent oxidation of LDL lipids. When pooled human plasma from 10 healthy volunteers was incubated in the presence of 25–100?μM either betanin or indicaxanthin, incorporation of both compounds in LDL was observed, with a maximum binding of 0.52±0.08, and 0.51±0.06?nmoles of indicaxanthin and betanin, respectively, per mg LDL protein. Indicaxanthin-enriched and betanin-enriched LDL were more resistant than homologous native LDL to copper-induced oxidation, as assessed by the elongation of the induction period. The incorporated indicaxanthin, however, appeared twice as effective as betanin in increasing the length of the lag phase, while both compounds did not affect the propagation rate. Both betalains were consumed during the inhibition period of lipid oxidation, and delayed consumption of LDL-beta carotene. Indicaxanthin, but not betanin, prevented vitamin E consumption at the beginning of LDL oxidation, and prolonged the time of its utilization. The resistance of LDL to oxidation when vitamin E and indicaxanthin acted separately in a sequence, was lower than that measured when they were allowed to act in combination, indicating some synergistic interaction between the two molecules. No prooxidant effect over a large concentration range of either betanin or indicaxanthin was observed, when either betalain was added to the LDL system undergoing a copper-induced oxidation.

These results show than indicaxanthin and betanin may bind to LDL, and are highly effective in preventing copper-induced lipid oxidation. Interaction with vitamin E appears to add a remarkable potential to indicaxanthin in the protection of LDL. Although molecular mechanisms remain uncompletely understood, various aspects of the action of betanin and indicaxanthin in preventing LDL lipid oxidation are discussed.     

Increased concentrations of circulating vitamin E in carriers of the apolipoprotein A5 gene - 1131T>C variant and associations with plasma lipids and lipid peroxidation

The aim of this study was to investigate the effects of the apolipoprotein A5 (APOA5) 1131T>C gene variant on vitamin E status and lipid profile. The gene variant was determined in 297 healthy nonsmoking men aged 20-75 years and recruited in the VITAGE Project. Effects of the genotype on vitamin E in plasma, LDL, and buccal mucosa cells (BMC) as well as on cholesterol and triglyceride (TG) concentrations in plasma and apolipoprotein A-I (apoA-I), apoB, apoE, apoC-III, and plasma fatty acids were determined. Plasma malondialdehyde concentrations as a marker of in vivo lipid peroxidation were determined. C allele carriers showed significantly higher TG, VLDL, and LDL in plasma, higher cholesterol in VLDL and intermediate density lipoprotein, and higher plasma fatty acids. Plasma alpha-tocopherol (but not gamma-tocopherol, LDL alpha- and gamma-tocopherol, or BMC total vitamin E) was increased significantly in C allele carriers compared with homozygote T allele carriers (P = 0.02), but not after adjustment for cholesterol or TG. Plasma malondialdehyde concentrations did not differ between genotypes. In conclusion, higher plasma lipids in the TC+CC genotype are efficiently protected against lipid peroxidation by higher alpha-tocopherol concentrations. Lipid-standardized vitamin E should be used to reliably assess vitamin E status in genetic association studies.