Reduction of platelet adhesiveness by vitamin E supplementation in humans

Vitamin E Supplement Protects Against Gestational Diabetes Mellitus in Mice Through nuclear factor-erythroid factor 2-related factor 2/heme oxygenase-1 Signaling Pathway

Background

Gestational diabetes mellitus (GDM) is the most common pregnant disorder worldwide. In this study, we aimed to explore whether vitamin E (VE) treatment alone could protect against GDM in a mouse model.

Methods

6-week-old C57BL/6J female mice were fed on high-fat diet for two weeks and continued with high-fat diet after pregnancy to induce GDM. The pregnant mice were orally administrated with 2.5, 25 or 250 mg/kg VE twice per day during pregnancy together with high-fat diet. Oral glucose tolerance test, insulin amounts, oxidative stress and inflammation were then measured.

Results

Only 250 mg/kg VE could improve glucose tolerance and insulin level in pregnant mice. VE (250 mg/kg) effectively inhibited GDM-induced hyperlipidemia, and secretion of inflammatory cytokines such as tumor necrosis factor-α and interleukin-6. VE also significantly ameliorated maternal oxidative stress at the late stage of pregnancy, and also improved reproductive outcomes, including increasing the litter size and birth weight in GDM mice. Moreover, VE also activated GDM-reduced nuclear factor-erythroid factor 2-related factor 2 (Nrf2) / heme oxygenase-1 signaling pathway in the maternal liver tissues of GDM mice.

Conclusion

Our data clearly demonstrated that 250 mg/kg VE twice a day during pregnancy could significantly ameliorate the symptoms of GDM by alleviating oxidative stress, inflammation, hyperglycemia, and hyperlipidemia through Nrf2/HO-1 signaling pathway in GDM mice. Thus, additional VE supplement might be beneficial to GDM.

10-year survival in coronary artery bypass grafting surgery patients in Tehran heart center, coronary outcome measurement study: Predictive power of dietary inflammatory index and dietary antioxidant quality

OBJECTIVES

There is a higher rate of mortality from cardiovascular disease (CVD) in Iran and the mortality rate increases even after coronary artery bypass grafting (CABG). The aim of this study was to evaluate the association between mortality and survival in patients 10 y after CABG, using the dietary inflammatory index (DII) and dietary antioxidant indices.

METHODS

In the current prospective cohort study, 450 patients with CVD who were referred to the Tehran Heart Center and who underwent an isolated CABG during the 6-mo period between April and September 2006 were enrolled. Anthropometric measurements and clinical assessments were performed. Biochemical assay, including hemoglobin A1c, serum lipids, creatinine, blood urea nitrogen, lipoprotein(a), albumin, and C-reactive protein, were also measured. DII, dietary antioxidant quality (DAQ) scores, and dietary Mediterranean quality index (MEDQI) were measured using the data obtained from a semi-quantitative food frequency questionnaire. Survival analysis was performed using the Kaplan-Meir method followed by log-rank test. The association between all-cause mortality and study parameters was performed with Cox proportional hazard model.

RESULTS

According to the present results, older ages, male sex, lower educational attainment, opium use, previous history of diabetes and myocardial infarction, and higher hematocrit and creatinine concentrations were associated with higher mortality rates. Among nutritional indices, a high inflammatory diet was a positive predictor of mortality, whereas a higher DAQ score was a negative predictor (P < 0.05). No association was found between the MEDQI score and mortality rate among patients.

CONCLUSION

According to the present findings, a diet high in inflammatory foods and low in antioxidant content is a potent predictor of mortality 10 y post-CABG. Therefore, reducing the inflammatory potential of the diet and improving its antioxidant content will be a preventive strategy for reducing mortality after CABG.

Tocotrienols-induced inhibition of platelet thrombus formation and platelet aggregation in stenosed canine coronary arteries

BACKGROUND

Dietary supplementation with tocotrienols has been shown to decrease the risk of coronary artery disease. Tocotrienols are plant-derived forms of vitamin E, which have potent anti-inflammatory, antioxidant, anticancer, hypocholesterolemic, and neuroprotective properties. Our objective in this study was to determine the extent to which tocotrienols inhibit platelet aggregation and reduce coronary thrombosis, a major risk factor for stroke in humans. The present study was carried out to determine the comparative effects of α-tocopherol, α-tocotrienol, or tocotrienol rich fraction (TRF; a mixture of α-+γ-+δ-tocotrienols) on in vivo platelet thrombosis and ex vivo platelet aggregation (PA) after intravenous injection in anesthetized dogs, by using a mechanically stenosed circumflex coronary artery model (Folts' cyclic flow model).

RESULTS

Collagen-induced platelet aggregation (PA) in platelet rich plasma (PRP) was decreased markedly after treatment with α-tocotrienol (59%; P<0.001) and TRF (92%; P<0.001). α-Tocopherol treatment was less effective, producing only a 22% (P<0.05) decrease in PA. Adenosine diphosphate-induced (ADP) PA was also decreased after treatment with α-tocotrienol (34%; P<0.05) and TRF (42%; P<0.025). These results also indicate that intravenously administered tocotrienols were significantly better than tocopherols in inhibiting cyclic flow reductions (CFRs), a measure of the acute platelet-mediated thrombus formation. Tocotrienols (TRF) given intravenously (10 mg/kg), abolished CFRs after a mean of 68 min (range 22 -130 min), and this abolition of CFRs was sustained throughout the monitoring period (50-160 min).Next, pharmacokinetic studies were carried out and tocol levels in canine plasma and platelets were measured. As expected, α-Tocopherol treatment increased levels of total tocopherols in post- vs pre-treatment specimens (57 vs 18 μg/mL in plasma, and 42 vs 10 μg/mL in platelets). However, treatment with α-tocopherol resulted in slightly decreased levels of tocotrienols in post- vs pre-treatment samples (1.4 vs 2.9 μg/mL in plasma and 2.3 vs 2.8 μg/mL in platelets). α-Tocotrienol treatment increased levels of both tocopherols and tocotrienols in post- vs pre-treatment samples (tocopherols, 45 vs 10 μg/mL in plasma and 28 vs 5 μg/mL in platelets; tocotrienols, 2.8 vs 0.9 μg/mL in plasma and 1.28 vs 1.02 μg/mL in platelets). Treatment with tocotrienols (TRF) also increased levels of tocopherols and tocotrienols in post- vs pre-treatment samples (tocopherols, 68 vs 20 μg/mL in plasma and 31.4 vs 7.9 μg/mL in platelets; tocotrienols, 8.6 vs 1.7 μg/mL in plasma and 3.8 vs 3.9 μg/mL in platelets).

CONCLUSIONS

The present results indicate that intravenously administered tocotrienols inhibited acute platelet-mediated thrombus formation, and collagen and ADP-induced platelet aggregation. α-Tocotrienols treatment induced increases in α-tocopherol levels of 4-fold and 6-fold in plasma and platelets, respectively. Interestingly, tocotrienols (TRF) treatment induced a less pronounced increase in the levels of tocotrienols in plasma and platelets, suggesting that intravenously administered tocotrienols may be converted to tocopherols. Tocotrienols, given intravenously, could potentially prevent pathological platelet thrombus formation and thus provide a therapeutic benefit in conditions such as stroke and myocardial infarction.

Vitamins and cardiovascular disease

CVD is a major cause of mortality and morbidity in the Western world. In recent years its importance has expanded internationally and it is believed that by 2020 it will be the biggest cause of mortality in the world, emphasising the importance to prevent or minimise this increase. A beneficial role for vitamins in CVD has long been explored but the data are still inconsistent. While being supported by observational studies, randomised controlled trials have not yet supported a role for vitamins in primary or secondary prevention of CVD and have in some cases even indicated increased mortality in those with pre-existing late-stage atherosclerosis. The superiority of combination therapy over single supplementation has been suggested but this has not been confirmed in trials. Studies have indicated that beta-carotene mediates pro-oxidant effects and it has been suggested that its negative effects may diminish the beneficial effects mediated by the other vitamins in the supplementation cocktail. The trials that used a combination of vitamins that include beta-carotene have been disappointing. However, vitamin E and vitamin C have in combination shown long-term anti-atherogenic effects but their combined effect on clinical endpoints has been inconsistent. Studies also suggest that vitamins would be beneficial to individuals who are antioxidant-deficient or exposed to increased levels of oxidative stress, for example, smokers, diabetics and elderly patients, emphasising the importance of subgroup targeting. Through defining the right population group and the optimal vitamin combination we could potentially find a future role for vitamins in CVD.

Anti-oxidant therapy: does it have a role in the treatment of human disease?

Free radical oxidative stress has been implicated in the pathogenesis of a variety of human diseases. Natural anti-oxidant defences have also been found to be defective in many of the same diseases. Many researchers have concluded that, if the imbalance between the oxidative stresses and anti-oxidant defence can be corrected by supplementing natural anti-oxidant defences, it may be possible to prevent or retard disease progression. Potential anti-oxidant therapies include natural anti-oxidant enzymes and vitamins or synthetic agents with anti-oxidant activity. Diseases where anti-oxidant therapy may be beneficial can be divided into those involving acute intervention, such as reperfusion injury or inflammation, and those involving chronic preventative therapy, such as atherosclerosis, carcinogenesis and diabetic vascular disease. The pharmaceutical considerations are different in each case. The principles guiding the development, use and assessment of anti-oxidant therapies are discussed in this review.

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.

Anti-oxidants-- a protective role in cardiovascular disease?

Established risk factors for cardiovascular disease (CVD), such as hypertension, smoking and diabetes mellitus, explain only some of the observed variation in clinical events. This has maintained interest in other nutritional and biochemical factors that might contribute to the underlying pathophysiology of CVD. All of these risk factors are associated with increased oxidative stress in the vessel wall, which may contribute to CVD by several mechanisms. Studies in animal models of CVD have suggested that natural and synthetic anti-oxidants can prevent the development of clinical end points. These observations have generated the hypothesis that anti-oxidant therapy might also prevent CVD in human populations. This has been supported by epidemiological studies showing a negative correlation between circulating concentrations or dietary intake of natural anti-oxidant vitamins and CVD event rate. Many studies have also demonstrated a beneficial effect of anti-oxidants on surrogate markers of CVD such as endothelial function and lipoprotein oxidation. However, the results of large prospective randomised controlled intervention trials, mostly involving vitamin E in patients at increased risk of CVD, have been disappointing and have failed to demonstrate the anticipated benefits. This paper will critically examine the evidence and try to offer some explanation for the apparent failure of animal and epidemiological data to translate into meaningful clinical benefits.

Vitamin E reduces platelet adhesion to human endothelial cells in vitro

Although it has been reported that vitamin E (alpha-tocopherol) can reduce platelet adhesiveness and aggregation in vivo, the mechanism is still unknown. Therefore, the aim of the present study was to determine whether incubations of platelet-rich plasma (PRP) with vitamin E influence platelet adhesion to cultured endothelial cells. To exclude blood plasma involvement, also washed platelets were pretreated with alpha-tocopherol. Vitamin E (0.5-1.0 mM) was added to PRP or washed platelets. Endothelial cells in monolayer were incubated with thrombin-activated platelets (1 or 2 U/ml). After 1 hr of incubation, non-adhered platelets were removed and counted. Treating of PRP with alpha-tocopherol inhibited platelet adhesion to endothelial cell monolayer. This effect was dose dependent on concentrations of alpha-tocopherol and thrombin. In our experiments PRP was treated with alpha-tocopherol and endothelial cell monolayer was used as test surface. These findings agree with previous observations on the adhesivity of platelets to synthetic surfaces after dietary vitamin E in healthy volunteers. When washed platelets were incubated with alpha-tocopherol, no significant reduction of adhesion was detectable. As preincubation of washed platelets with alpha-tocopherol does not inhibit platelet adhesion, it may be supposed that the effect of vitamin E does not occur in a directly cellular mechanism. The data suggest that alpha-tocopherol may reduce platelet adhesiveness probably after incorporation by plasma lipoproteins.

Study design and baseline characteristics of the study to evaluate carotid ultrasound changes in patients treated with ramipril and vitamin E: SECURE

Atherosclerotic cardiovascular disease remains a major cause of mortality and morbidity in most developed countries. Experimental and clinical evidence suggests that angiotensin-converting enzyme inhibitors and vitamin E therapy may retard the atherosclerotic process; however, definitive proof in humans is lacking. The Study to Evaluate Carotid Ultrasound Changes in Patients Treated with Ramipril and Vitamin E (SECURE) is designed to assess the effects of ramipril--an angiotensin-converting enzyme inhibitor, at 2 doses: 2.5 mg daily (which has little effect on lowering blood pressure) and 10 mg daily--and the antioxidant vitamin E, 400 IU daily, on atherosclerosis progression in 732 patients using a factorial 3 x 2 study design. High-risk patients with a documented history of significant cardiovascular disease or with diabetes and additional risk factors were enrolled and will be followed for 4 years. The extent and progression of atherosclerosis are assessed noninvasively by B-mode carotid ultrasonography. The SECURE trial is a substudy of the larger Heart Outcomes Prevention Evaluation (HOPE) study of 9,541 high-risk patients evaluating the effects of ramipril and vitamin E on major cardiovascular events (cardiovascular death, myocardial infarction, and stroke). The 2 studies are complementary. Whereas HOPE is expected to provide information on major clinical outcomes, SECURE will shed light on the mechanisms by which these effects may be mediated.

Effects on health of dietary supplementation with 100 mg d-alpha-tocopheryl acetate, daily for 6 years

To evaluate the clinical antioxidant effects of vitamin E, 161 healthy volunteers aged 39 to 56 years, were given 100 or 3 mg of d-alpha-tocopheryl acetate orally daily for 6 years using a randomized, double-blind design. Among the 147 volunteers who qualified for the analysis, seven of the 73 volunteers receiving 3 mg d-alpha-tocopheryl acetate daily and none of the 74 volunteers receiving 100 mg had coronary disorders including myocardial damage (P < 0.02). ST or T wave abnormalities on electrocardiograms were considered to indicate coronary disorders (four volunteers). The mean serum total tocopherol (TOC) concentration in the 100-mg group was significantly higher than that in the 3-mg group 6 months after the start of the study, and this raised value was maintained throughout the study; the level in the 3-mg group did not change significantly from the baseline value. The low-density lipoprotein cholesterol/total TOC ratio, a parameter of the inhibition of peroxidation of low-density lipoprotein cholesterol, was the only serum lipid parameter that was significantly different, at baseline, in the volunteers with coronary disorders compared with the others. These findings indicate that long-term supplementation with 100 mg tocopheryl acetate daily may prevent the early stages of coronary atherosclerosis by decreasing peroxidation of low-density lipoprotein cholesterol.

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.

Abnormalities of retinal metabolism in diabetes or galactosemia. II. Comparison of gamma-glutamyl transpeptidase in retina and cerebral cortex, and effects of antioxidant therapy

Levels of the intracellular antioxidant, glutathione, become subnormal in retina in diabetes or experimental galactosemia. In order to investigate the cause and significance of this abnormality, activity of gamma-glutamyl transpeptidase (an enzyme important in the synthesis and degradation of glutathione) and levels of reduced glutathione have been measured in retinas of diabetic rats and dogs and of experimentally galactosemic rats and dogs. Retinal gamma-glutamyl transpeptidase activity and glutathione level were significantly less than normal after 2 months of diabetes or galactosemia. In contrast, cerebral cortex from the same diabetic rats and galactosemic rats showed no significant reduction in either gamma-glutamyl transpeptidase activity or glutathione level. These different responses of the two tissues to hyperglycemia might help account for the difference in microvascular disease in these two tissues in diabetes. Consumption of the antioxidants, ascorbic acid (1.0%) plus alpha-tocopherol (0.1%), by diabetic rats and galactosemic rats inhibited the decrease of gamma-glutamyl transpeptidase activity and glutathione levels in retina, suggesting that defects in glutathione regulation in the retina are secondary to hyperglycemia-induced 'oxidative stress'.

Prevention of platelet dysfunction by vitamin E in diabetic atherosclerosis

Premature atherosclerosis and other vascular disorders are serious complications of diabetes mellitus. Contributing factors include (i) increased peroxidation of LDL leading to foam cell formation, fatty streaks and plaque formation in the arterial wall, and (ii) hyperreactivity of blood platelets leading to increased platelet adhesion and aggregation. Vitamin E may play a protective role as an antioxidant and/or membrane stabilizing agent in either mechanism. In platelets it appears to regulate arachidonic acid metabolism. Decreased vitamin E levels in platelets are associated with increased aggregation. This is reversible by correction of the vitamin E status. In diabetics, platelet vitamin E levels tend to be reduced with concomitant increase in platelet aggregation. Several studies in patients with insulin-dependent diabetes mellitus and, to some extent, in those with non-insulin-dependent diabetes mellitus have shown that supplementation with several hundred IU vitamin E significantly reduced platelet aggregation and lipid peroxidation. In healthy volunteers high-dose supplementation had no notable effect on platelet aggregation. However, doses as low as 200 IU vitamin E significantly reduced platelet adhesion and inhibited the formation of protruding pseudopods typically occurring in activated platelets. In diabetic patients a decrease in the nonenzymatic glycation of proteins by vitamin E supplementation has been observed. Controlled studies are needed to confirm the effect of vitamin E on platelet function in well-defined groups of diabetics, followed by large-scale trials investigating the prevention of diabetic vascular complications as clinical end point.

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.

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.

Effect of dietary menhaden, Canola and partially hydrogenated soy oil supplemented with vitamin E upon plasma lipids and platelet aggregation

Male Fisher rats were fed chow diets for two weeks after which they were divided into seven groups of ten rats each and fed 20% Canola, 20% menhaden, 20% partially hydrogenated soy oil (PHSO) or chow only, with or without 500 mg/Kg dietary vitamin E in chow containing 2% cholesterol for six weeks. Triglycerides were lower in the menhaden group and were essentially the same in the E supplemented groups as in their unsupplemented cohorts. Plasma cholesterol was higher in the Canola, and lower in the menhaden, groups, compared to the PHSO group. Cholesterol was the same in the E supplemented groups as in their unsupplemented cohorts. Plasma thiobarbituric acid reactant substances (TBARS) were higher in the menhaden group, compared to the chow group. Vitamin E supplementation lowered TBARS in the menhaden and PHSO groups, compared to the unsupplemented cohorts. Collagen induced platelet aggregation was lower in both Canola and menhaden groups, compared to the PHSO group. Vitamin E supplementation lowered collagen induced platelet aggregation only in the PHSO group. Thrombin induced platelet aggregation was lower in the Canola group, compared to the PHSO group. Vitamin E supplementation did not affect thrombin induced platelet aggregation compared to unsupplemented cohorts. Plasma vitamin E levels were lowest in the menhaden supplemented group compared to all other groups not receiving E, suggesting a greater requirement for E in this group. Finally, vitamin E supplementation raised the plasma E levels in all groups except the menhaden group when compared to unsupplemented cohorts.

Unequal distribution of membrane components between pseudopodia and cell bodies of platelets

Platelet pseudopodia were compared to platelet cell bodies with respect to their lipid composition, fatty acid distribution and protein composition. The methodology for producing pseudopodial preparations of platelets stimulated with thrombin, ADP or calcium ionophore was established. The separation of pseudopodia and cell bodies was verified by electron microscopic examination of the respective platelet components. Lipid analyses demonstrated a preponderance of lysophospholipids and sphingomyelin in pseudopodial preparations and a large increase in mono-, di- and tri-ene fatty acids as compared to cell bodies. Changes were also evident in the protein composition evaluated by one- and two-dimensional SDS-polyacrylamide gel electrophoresis and by [32P]ATP labeling of exofacial membrane proteins. A protein of approximately 68 kDa which reacted strongly with antibody to PlA1, was prominantly displayed in platelet pseudopodia. Thus, our studies demonstrate a heterogeneous distribution of lipids and proteins in a mammalian membrane system which may have important implications for the functional behavior of the cell.

Short term vitamin E supplementation has no effect on platelet function, plasma phospholipase A2 and lyso-PAF in male volunteers

1. Based largely upon in vitro studies, vitamin E has been reported to inhibit phospholipase A2 activity, to alter phospholipid metabolism and reduce platelet aggregation. 2. The effect of dietary supplementation with D-alpha-tocopherol (1500 iu/day for 14 days) was studied in nine males, 41-63 years old, comparing active treatment with a preceding placebo period. 3. Despite an increase from 2.6 +/- 0.8 (s.d.) x 10(-5) mol/L to 6.0 +/- 1.8 10(-5) mol/L in plasma vitamin E there were no significant changes in the aggregation of diluted whole blood or platelet rich plasma to adenosine diphosphate (ADP) or collagen, in plasma phospholipase A2 activity or plasma lyso-platelet-activating factor (lyso-PAF) (bioassay after in vitro acetylation to PAF). 4. High dose vitamin E dietary supplementation had no effect on these phospholipid and platelet parameters.

Effect of dietary canola and reference oils upon serum lipids and platelet aggregation

To compare Canola a terrestrial (n-3) oil with fish oil (n-3) and common vegetable oil (n-6) in decreasing serum lipids and platelet aggregation, various oils were included in Chow-based diets and fed to rats in an eight-weeks feeding trial. The Chow diet contained 2% cholesterol along with either Canola, menhaden, safflower, or partially hydrogenated soy oil, or no oil addendum. The menhaden oil group was the only one to show a significant reduction in serum cholesterol and triglycerides and at the same time yielded the most uniform decrease in platelet aggregability. However, this same group was also the only one to show a decrease in serum tocopherol levels, suggesting that improving an atherogenic risk profile may require antioxidant supplementation. In these rat trials, Canola oil supplementation did not yield the same results measured during menhaden supplementation.

Plasma vitamins E and A inversely correlated to mortality from ischemic heart disease in cross-cultural epidemiology

In eight study populations in which the medians of total plasma cholesterol did not differ significantly (mean 5.8 mM, p greater than 0.05) and therefore did not correlate with the IHD mortality (r2 = 0.05), the median of absolute plasma level of vitamin E (alpha-tocopherol) was inversely related to the IHD mortality (r2 = 0.55; p = 0.003). Vitamin A behaved similarly (r2 = 0.51; p = 0.046). The absolute levels of vitamins E and A together with cholesterol predicted (by multiple regression analysis) the IHD mortality of these eight populations fairly well (r2 = 0.81; p = 0.06). Considering all 12 study populations analyzed thus far, total plasma cholesterol correlated with the IHD mortality directly as expected (r2 = 0.51; p less than 0.01), but the median of the plasma alpha-tocopherol individually standardized for cholesterol and triglycerides (220 mg/dL + 110 mg/dL, respectively) maintained a strong inverse association with the IHD mortality (r2 = 0.49; p = 0.01). In the partial regression analysis, lipid-standardized vitamin E exhibited an even stronger inverse correlation with IHD mortality (r2 = 0.69; p less than 0.001). Again, vitamin A behaved similarly to vitamin E, that is, after lipid-standardization of individuals (r2 = 0.33; p = 0.07), as well as in the cholesterol-independent partial regression analysis (r2 = 0.74; p less than 0.001). Both vitamins may act singularly, for after lipid-standardization they vary de facto independently (rs = 0.012) in individuals. The combination of vitamins E and A as obtained by multiple partial regression predicted the actual IHD mortality to a large extent (r2 = 0.89; p less than 0.001), whereas the three-variable prediction model, with the median of total cholesterol and of individually lipid-standardized vitamins E and A, fit the actual IHD mortality of these 12 populations almost completely (r2 = 0.94; p less than 0.001). In conclusion, the plasma status of vitamins E and A are important, hitherto underrated risk factors of IHD, which may act independently, but can, if combined, predict at least 53% of the cross-cultural differences of IHD mortality. After inclusion of total cholesterol into a multivariate model, up to 94% of the IHD mortality can be predicted. The present epidemiological data are in agreement with the hypothesis that these vitamins have physiological functions in the protection of lipoproteins against peroxidation and atherogenic apo-B modifications, respectively, but that does not exclude additional beneficial effects of vitamin E and A in the arterial wall.

Alpha-tocopherol, a potent modulator of endothelial cell function

The effect of alpha-tocopherol on various endothelial cell functions was evaluated in vitro using cultures of human umbilical vein endothelial cells. Prostacyclin synthesis, plasminogen activator activity and von Willebrand factor activity were evaluated in control and alpha-tocopherol supplemented cultures. Alpha-tocopherol produced stimulation of prostacyclin production which peaked at or near 0.5 mM. Plasminogen activator activity was markedly reduced by the addition of alpha-tocopherol. Von Willebrand factor activity showed a significant decrease of processed and cellular forms that was dose-dependent. The incorporation of alpha-tocopherol into endothelial cells could be demonstrated by measuring intracellular levels of the vitamin in washed endothelial cells. Our results show that alpha-tocopherol has a profound effect on multiple endothelial cell functions which are intimately involved in hemostasis.