Alpha-tocopherol, a potent modulator of endothelial cell function

Von Willebrand Factor and Autoantibodies against Oxidized LDL in Hemodialysis Patients Treated with Vitamin E-Modified Dialyzers

Oxidant stress is a well known cause of damage in the atherosclerotic process. Vitamin E is one of the most promising natural antioxidants. In this study we investigated if a vitamin E-coated dialyzer was able to reduce the plasma levels of auto-antibodies against oxidized-LDL, von Willebrand factor (vWf) and thrombomodulin (TM) as markers of endothelial damage.

In this controlled 6-month prospective study, we investigated these markers in two matched groups (n= 16 each) of patients on regular hemodialysis not yet diagnosed for atherosclerosis cardiovascular disease (ACVD) (mean age= 58.3±7.0 yrs, mean dialysis age = 30.1±10.0 months), in which cellulosic (CLS) and vitamin E-modified dialyzers (CLE) were compared. At inclusion all the patients were treated with CLS. Then, the study group was shifted to CLE for 6 months.

At baseline the patients showed normal levels of vitamin E and high levels of oxLDL-Ab, vWf and TM compared to healthy subjects. In the CLE group oxLDL-Ab and vWf, but not TM levels, decreased progressively (from 472±287 to 264±199 mU/mL, p<0.0001 and from 101.1±7.5% to 76.7±18.5%; p<0.001, respectively), and vitamin E increased from 4.40±0.81 to 7.81±1.16 μg/mg of cholesterol. At the end of the study, 8 of the patients treated with CLE were randomly selected and went back to the membrane without Vitamin E for six months. They showed an significant increase in OxLDL-Ab and vWf levels and a significant reduction in tocoferol levels. In conclusion, CLE compared to cellulosic dialyzers can lower some indices of damage to LDL and endothelial cells.

Effects of vitamin E supplementation on exercise-induced oxidative stress: a meta-analysis

Tocopherols (commonly referred to as “vitamin E”) are frequently studied antioxidants in exercise research. However, the studies are highly heterogeneous, which has resulted in contradicting opinions. The aim of this review is to identify similar studies investigating the effects of tocopherol supplementation on exercise performance and oxidative stress and to perform minimally biased qualitative comparisons and meta-analysis. The literature search and study selection were performed according to Cochrane guidelines. A 2-dimensional study execution process was developed to enable selection of similar and comparable studies. Twenty relevant studies were identified. The high variability of study designs resulted in final selection of 6 maximally relevant studies. Markers of lipid peroxidation (malondialdehyde) and muscle damage (creatine kinase) were the 2 most frequently and similarly measured variables. Meta comparison showed that tocopherol supplementation did not result in significant protection against either exercise-induced lipid peroxidation or muscle damage. The complex antioxidant nature of tocopherols and low accumulation rates in muscle tissues could underlie an absence of protective effects.

Cellular, molecular and clinical aspects of vitamin E on atherosclerosis prevention

Randomised clinical trials and epidemiologic studies addressing the preventive effects of vitamin E supplementation against cardiovascular disease reported both positive and negative effects, and recent meta-analyses of the clinical studies were rather disappointing. In contrast to that, many animal studies clearly show a preventive action of vitamin E in several experimental settings, which can be explained by the molecular and cellular effects of vitamin E observed in cell cultures. This review is focusing on the molecular effects of vitamin E on the cells playing a role during atherosclerosis, in particular on the endothelial cells, vascular smooth muscle cells, monocytes/macrophages, T cells, and mast cells. Vitamin E may act by normalizing aberrant signal transduction and gene expression in antioxidant and non-antioxidant manners; in particular, over-expression of scavenger receptors and consequent foam cell formation can be prevented by vitamin E. In addition to that, the cellular effects of alpha-tocopheryl phosphate and of EPC-K1, a composite molecule between alpha-tocopheryl phosphate and l-ascorbic acid, are summarized.

Vitamin E in renal therapeutic regiments

Administration of vitamin E in children with immunoglobulin A (IgA) nephropathy, focal segmental glomerulosclerosis (FSGS) and type I diabetes demonstrated potential towards ameliorating progression. Oral vitamin E therapy reduced endothelial dysfunction, lipid peroxidation and oxidative stress in patients with chronic kidney failure (CKF). Moreover, the use of vitamin E-bonded hemodialyzers reduced atherosclerotic changes, erythropoietin dosage and muscular cramps in patients on hemodialysis (HD). However, several controlled clinical trials failed to document beneficial effects on the study subjects' cardiovascular and renal outcomes. A recent report of increased all-cause mortality in adult patients receiving high dose vitamin E therapy has caused considerable concern and debate. These issues regarding the efficacy and safety of vitamin E in renal therapeutic regimens will be reviewed in this article.

9-trans, 11-trans-CLA: antiproliferative and proapoptotic effects on bovine endothelial cells

Endothelial cell function can be influenced by nutrition, especially dietary FA and antioxidants. One class of dietary FA that is found in meat and dairy products derived from ruminant animals is conjugated linoleic acids (CLA). We have examined the effects of several CLA isomers on endothelial cell proliferation. 9t,11t-CLA was the only isomer that inhibited bovine aortic endothelial cell (BAEC) [3H]methylthymidine incorporation (I50 = 35 microM), and this antiproliferative effect was time-dependent. A small decrease (20%) in cell number was observed only at the highest concentration (60 microM) tested. The 9c,11t-, 9c,11c-, 10t 12c-, and 11c,13t-CLA isomers did not exhibit any antiproliferative effects over a 5-60 microM concentration range. alpha-Tocopherol and BHT decreased BAEC proliferation, but pretreatment of cells with either of these antioxidants substantially attenuated the antiproliferative effect of 9t,11 t-CLA. No difference in lipid peroxidation, as measured by the thiobarbituric acid assay for malondialdehyde, was observed on treatment of endothelial cells with either 9t,11 t- or 9c,11 t-CLA. However, a 43% increase in caspase-3 activity was observed after incubating BAEC with 9t,11 t-CLA, suggesting that the antiproliferative effect of this isomer is partially due to an apoptotic pathway. In contrast to the above results with normal endothelial cells, these five CLA isomers all inhibited proliferation of the human leukemic cell line THP-1, with the 9t,11 t isomer again being the most (I50 = 60 microM) effective. These results confirm that different CLA isomers have different inhibitory potencies on the proliferation of normal and leukemic cells.

The effects of vitamin E on platelet activity in β-thalassaemia patients

A double-blind, crossover, placebo-controlled study of the effect of vitamin E on platelet functions was performed on nine splenectomized and 16 non-splenectomized beta-thalassaemia/haemoglobin E (beta-thalassaemia/HbE) patients. The patients were supplemented with a daily dose of vitamin E (525 IU) for 3 months. The functions of platelets were assessed by adenosine diphosphate (ADP)-induced platelet aggregation and adenosine triphosphate release. Plasma alpha-tocopherol, plasma thiobarbituric reactive substances (TBARs) and serum ferritin levels represented patients' antioxidant status, lipid peroxidation status and iron status respectively. Before experimentation, all patients had low plasma alpha-tocopherol levels. The splenectomized patients showed severe iron overload iron, had higher plasma TBAR levels and their platelets were more reactive to ADP than those of non-splenectomized patients. Three months of daily vitamin E supplementation resulted in a significant increase in plasma alpha-tocopherol levels and reduction in plasma TBAR levels in all patients. Serum ferritin levels of the patients were not altered; however, vitamin E reduced the platelet reactivity of the splenectomized patients towards normal levels. The influence of vitamin E on platelet reactivity may result in delaying hypoxaemia and pulmonary occlusion that commonly occurs in splenectomized beta-thalassaemia/HbE patients.

Quantitative analysis of vitamin E, cholesterol and phospholipid fatty acids in a single aliquot of human platelets and cultured endothelial cells

A reliable procedure is described for the joint analysis of vitamin E (tocopherols), cholesterol and phospholipids in the same minute sample of human platelets and on human cultured endothelial cells. The whole procedure is based on the extraction of total lipids, thin-layer chromatography of all compounds of interest and microcolumn purification of tocopherols and cholesterol. The combined use of butyl hydroxytoluene and ascorbic acid in the purification steps allowed a complete recovery of the tocopherols analyzed, as well as of cholesterol by high-performance liquid chromatography. The detection of these lipids was performed with fluorometric, spectrophotometric and evaporative light-scattering detectors whose respective sensitivities were compared. The fatty acid composition of phospholipid classes from the same sample, separated on the same silica gel plate, was determined by gas-liquid chromatography. The whole procedure is rapid since it requires about 4 h to analyse tocopherols and cholesterol and to prepare methylated fatty acids, 28 samples being easily completed within one working day. The evaluation of the whole membrane antioxidant status requires as little as one 25 cm2 confluent culture flask (about 0.75 x 10(6) cells) for endothelial cells or two ml of blood (3 x 10(8) platelets).

Effect of vitamin E on human aortic endothelial cell responses to oxidative injury

Reactive oxygen species produced by the cells present in the arterial wall may cause oxidative damage to cellular components altering endothelial cell (EC) function. Changes in the EC function appear to play a key role in the pathogenesis of atherosclerosis. Human aortic endothelial cells (HAEC) were employed to investigate the protective role of vitamin E upon exposure of endothelial cells to oxidative stress in vitro. HAEC assimilate d-alpha-tocopherol from the media in a dose-dependent manner. Exposure of HAEC to 16.5 mM of the free radical generator 2,2'-azobis (2-amidinopropane) hydrochloride (AAPH) for 16 h decreased cell viability (assessed by trypan blue exclusion) from 90 to 28%. HAEC preincubated with vitamin E at 15, 30, and 60 microM prior to the AAPH exposure resulted in a dose-dependent increase in resistance to oxidative stress and increased cell viability by 37, 66, and 85%, respectively. An increase in prostacyclin (PGI2) production by HAEC in response to AAPH exposure was correlated positively with cell damage and negatively with vitamin E concentration. Interleukin (IL)-1 production also increased in parallel with cell damage induced by AAPH. Vitamin E treatment significantly reduced IL-1 production after AAPH exposure. This modulatory role of vitamin E on HAEC function following exposure to an oxidative stress may reflect its antioxidant protection against lipid peroxidation.

Experimental thrombosis model induced by free radicals. Application to aspirin and other different substances

A large number of experimental studies suggests that oxygen free radicals play a major role in the pathogenesis of the myocardial lesions observed during the sequence ischemia-reperfusion. The purpose of this study was to determine whether oxygen free radicals can induce thrombosis. In so doing we have developed a new experimental thrombosis model. Reproducible focal thrombosis has been achieved by irradiating mesenteric arterioles of rat for variable time with green filtered light issuing from a mercury lamp after systemic injection of different rose bengal doses. The number of emboli that remove in the blood (N), the duration of total occlusion (T) and the number of emboli per minute were then measured. As control, no rose bengal administration was done and the vessels were exposed to the filtered light. In comparison with this control, results clearly showed that free radicals always induced thrombosis and the induced thrombus was mainly composed of platelets. In this new thrombosis model induced by free radicals antithrombotic drugs (aspirin, 200 mg/Kg, heparin, 2 mg/Kg) and antioxidants (vitamin C, 10 and 20 mg/Kg, allopurinol, 200 and 300 mg/Kg, vitamin E, 500 and 1000 mg/Kg) have been tested. Results have shown that only heparin and vitamin E had an antithrombotic effect on thrombus formation induced by free radicals. This model should be useful in studying the effects of different drugs and could lead to new treatment modalities for ischemic accident and other cardiovascular diseases.

Effects of anti-oxidant treatment on sciatic nerve dysfunction in streptozotocin-diabetic rats; comparison with essential fatty acids

In Study 1, the effects of treatment of streptozotocin-diabetic rats with the antioxidants, probucol or vitamin E were compared. Untreated diabetic rats showed a reduction of 45% (p < 0.01) in nerve laser Doppler flux, which was used as an index of nerve blood flow. In diabetic rats treated with either probucol or vitamin E nerve Doppler flux was reduced by only 13 or 16%, respectively (p < 0.01 for either compared to untreated diabetic rats). A second study examined the effects of treatment with evening primrose oil either alone or in combination with probucol. Reduced nerve Doppler flux was reproduced in untreated diabetic rats (47%; p < 0.01). In parallel diabetic groups, nerve Doppler flux was reduced by only 14% with evening primrose oil alone and by 8% with evening primrose oil plus probucol (both p < 0.01 vs untreated diabetic rats). Both treatments were also associated with marked attenuation of motor and sensory nerve conduction velocity deficits. Measurements on plasma from rats showed normalisation of triglyceride levels by probucol treatment without an effect on those of cholesterol in Study 1. In Study 2, the converse was true for evening primrose oil treatment, whilst the combined treatment lowered both plasma triglycerides and cholesterol. This work indicates similar effects of antioxidants and evening primrose oil against reduced nerve Doppler flux and conduction velocity in diabetic rats, with dissimilar actions on plasma triglycerides and cholesterol.

The role of vitamin E in normal and damaged skin

The generation of free oxygen radicals is believed to play an important pathogenic role in the development of various disorders. More than other tissues, the skin is exposed to numerous environmental chemical and physical agents such as ultraviolet light causing oxidative stress. In the skin this results in several short- and long-term adverse effects such as erythema, edema, skin thickening, wrinkling, and an increased incidence of skin cancer or precursor lesions. However, accelerated cutaneous aging under the influence of ultraviolet light, usually termed photoaging, is only one of the harmful effects of continual oxygen radical production in the skin. Others include cutaneous inflammation, autoimmunological processes, keratinization disturbances, and vasculitis. Vitamin E is the major naturally occurring lipid-soluble non-enzymatic antioxidant protecting skin from the adverse effects of oxidative stress including photoaging. Its chemistry and its physiological function as a major antioxidative and anti-inflammatory agent, in particular with respect to its photoprotective, antiphotoaging properties, are described by summarizing animal studies, in vivo tests on human skin and biochemical in vitro investigations. The possible therapeutic use in different cutaneous disorders, and pharmacological and toxicological aspects are discussed. Many studies document that vitamin E occupies a central position as a highly efficient antioxidant, thereby providing possibilities to decrease the frequency and severity of pathological events in the skin. For this purpose increased efforts in developing appropriate systemic and local pharmacological preparations of vitamin E are required.

Recovery after dietary vitamin E supplementation of impaired endothelial function in vitamin E-deficient rats

1. Thoracic aortae, isolated from rats supplemented with dietary vitamin E after vitamin E deficiency, were analysed for changes in vascular reactivity. 2. Following 4 or 12 months of dietary vitamin E deficiency, endothelium-dependent vasodilator responses to acetylcholine were significantly impaired. However, when animals were fed after the first 4 months of vitamin E deprivation with a vitamin E-supplemented diet for 8 months, endothelium-mediated responses were completely restored. 3. In contrast, the endothelium-independent vasodilator or vasoconstrictor responses to sodium nitroprusside and noradrenaline, respectively were not altered either by vitamin E deficiency or supplementation. 4. These data indicate that vitamin E supplementation reversed the impairment of endothelial cell function which occurs during vitamin E deficiency.

Thioallyl compounds: potent inhibitors of cell proliferation

S-Allylmercaptocysteine was shown to inhibit vascular smooth-muscle and umbilical endothelial cell proliferation. Inhibition was dose-dependent and affected smooth-muscle cells more than endothelial cells. S-Allylmercaptocysteine was two orders of magnitude more potent than S-allylcysteine and cells grown in its presence showed distinct changes in their phosphorylation compared to untreated controls. Among the proteins whose phosphorylation was altered were GTP-activating protein, protein tyrosine phosphatase-1B and p34cdc2. We conclude that thioallyl compounds, natural constituents of garlic and known to inhibit malignant cells, can also reduce the proliferation of normal cells.

Some aspects of vitamin E related to humans and breast cancer prevention

The biological activities of vitamin E are related to the cellular functions and presence of sufficient tissue concentrations of this micronutrient. Most of the stored vitamin E is in the adipose tissue where it appears to be distributed equally. The breast adipose tissue has similar vitamin E concentrations as other parts of the body. The ductal systems also store vitamin E in sufficient concentrations to maintain cellular functions. The milk secreted from the ducts of the breast contains a high concentration of tocopherol. Whereas the normal breast tissue presumably utilizes vitamin E as an antioxidant, tumor tissue appears to handle vitamin E differently. Breast tumors possessing estrogen negative receptors and having poor histological differentiation have lower concentrations of vitamin E than tumors with positive estrogen receptors and well differentiated histology. Since vitamin E is considered the principal, if not sole, chain-breaking lipophilic antioxidant in plasma and tissue, its role as a potential chemopreventive agent in breast cancer should be further investigated. The combination of vitamin E with other cancer chemopreventive agents appears to be a reasonable procedure.

Therapeutic potential of vitamin E in the pathogenesis of spontaneous atherosclerosis

Spontaneous atherosclerosis is largely an occlusive disease of medium-size arteries whose progression in a hyperlipidemic environment reflects chronic interactions among injury stimuli to the vessel wall and "responses to injury" by vascular tissue and certain blood components. Development of vessel lesions in animal models of spontaneous atherosclerosis and (at least in principle) in man largely reflects responses of three major cell types (vascular endothelial cells, vascular smooth muscle cells, monocytes-macrophages) as well as the content and distribution of lipids among various lipoprotein subclasses and the increased atherogenicity of modified (e.g., oxidized) lipoproteins. The severe clinical complications associated with spontaneous atherosclerosis, along with its rather common incidence in man, have focused attention on the prevention and therapy of this vascular disease state. Some pharmacological studies in animal models of spontaneous atherosclerosis and some retrospective epidemiological studies in man suggest that vitamin E, the principal (if not sole) lipid-soluble chain-breaking tissue antioxidant, might have therapeutic benefit as an antiatherosclerotic agent. This suggestion gains support from a variety of compelling in vitro evidence demonstrating direct influences of vitamin E on cells and lipoproteins likely involved in the pathogenesis of spontaneous atherosclerosis. Biochemical and cellular data indicate that the potential antiatherogenic activity of vitamin E could reflect its activities as a regulator of endothelial, smooth muscle, or monocyte-macrophage function, an inhibitor of endothelial membrane lipid peroxidation, a modulator of plasma lipid levels and lipid distribution among circulating lipoproteins, and a preventor of lipoprotein oxidative modification. On the other hand, there is a comparative lack of conclusive evidence from animal models regarding: (a) the importance to atherogenesis of vascular and cellular processes modulated by vitamin E; (b) the influence of vitamin E on these processes in vivo and, consequently, on the initiation/progression of spontaneous atherosclerosis. Therefore, pharmacologic investigation of vitamin E (and synthetic, vitamin E-like antioxidants) in nutritional and hyperlipidemic animal models of spontaneous atherosclerosis is required to establish whether any atherosclerotic impact is associated with vitamin E and, if so, what the mechanistic basis of the therapeutic benefit is. Such a line of experimental inquiry should also increase our understanding of the pathogenesis of atherosclerotic vessel disease per se.

The effect of sulphinpyrazone and alpha-tocopherol on platelet activation and function in haemodialysed patients

In 30 patients on chronic haemodialysis treatment the platelet activity and function were studied before and during antiplatelet therapy with alpha-tocopherol and sulphinpyrazone. In both kinds of treatment a significant decrease of ADP-induced and spontaneous aggregation was observed. Sulphinpyrazone exerts an inhibitory effect not only on platelet aggregation but also on platelet factor 3 and provokes a significant prolongation of the bleeding time.