Modulation by dietary vitamin E and selenium of clotting whole blood thromboxane A2 and aortic prostacyclin synthesis in rats

Long-term vitamin E supplementation reduces atherosclerosis and mortality in Ldlr-/- mice, but not when fed Western style diet

OBJECTIVES

Epidemiological and experimental evidence have indicated potential health benefits of vitamin E supplementation on coronary heart disease (CHD), but several clinical trials have reported no benefit from vitamin E supplementation on CHD. We hypothesized that supplemental intake of vitamin E from an early age may prevent or retard the development and progression of atherosclerosis and CHD mortality.

METHODS

To test this hypothesis, 300 Ldlr(-/-) mice were divided into groups receiving Western style high fat/cholesterol (HFHC), moderate fat/cholesterol (MFMC), or low fat/cholesterol (LFLC) diets all containing 50 IU of vitamin E. These dietary groups were further subdivided into four sub-groups (n = 25) receiving their respective diets with no vitamin E supplementation or additionally supplemented with vitamin E (500 IU/kg diet) starting at the early age of 5 wks, or 6 mo, or 12 mo. All mice remained on their assigned diets until age 18 mo. Body weight, health status and survival rate of mice were monitored and recorded. After 18 mo of dietary treatments, mice were sacrificed.

RESULTS

Body weight was the highest in HFHC groups and the lowest in LFLC groups. Plasma concentration of cholesterol and triglycerides was high in all dietary groups, and plasma vitamin E was high in vitamin E supplemented groups. Fifty percent of mice fed Western style HFHC diet and 53% of mice fed MFMC diet survived during the 18 mo, whereas 75% of mice fed LFLC diet survived during the 18 mo dietary treatments. At the age of 18 mo, all the Ldlr(-/-) mice, regardless of dietary treatments, had several advanced atherosclerotic lesions in both aortic root and aortic tree. Within the LFLC groups, those that received vitamin E supplements from age 5 wks up to 18 mo had a significantly higher survival rate of 88% (p = 0.04) and lower mortality (12%) compared to mice that did not receive vitamin E supplements (64%). This lower mortality rate and higher survival rate coincided with significantly (p = 0.03) fewer aortic lesions in the vitamin E supplemented LFLC group (50%) compared to LFLC mice that did not receive vitamin E supplements in their diets (65%). Subjective immunohistochemical evaluation of aortic valves showed that LFLC mice that received vitamin E supplements for 18 mo had less intima media thickness compared to LFLC mice that did not receive vitamin E supplements in their diet. The LFLC mice that were supplemented with vitamin E for 18 mo had the lowest mRNA expression of inflammatory markers such as VCAM-1, MCP-1 and CD36 in samples obtained from lesion and non-lesionareas.

CONCLUSION

In conclusion, 500 mg vitamin E/kg diet in Ldlr(-/-) mice is not effective at reducing mortality and atherosclerosis when the diet contained high or medium levels of fat and cholesterol. However, a relatively low dose and long-term vitamin E supplementation started from an early age is effective in reducing mortality and atherosclerotic lesions in genetically prone Ldlr(-/-) mice fed LFLC diet.

Vitamin E and atherosclerosis: beyond prevention of LDL oxidation

Atherosclerosis is a chronic inflammatory disease of the arterial wall. Observational and experimental studies indicate that dietary vitamin E supplementation is associated with reduced risk of atherosclerosis. Evidence indicates that vitamin E, in addition to inhibition of oxidative modification of LDL, may inhibit atherogenesis through several other mechanisms at the molecular and cellular levels, which also include its nonantioxidant functions.

Tocotrienol: a review of its therapeutic potential

OBJECTIVES

To summarize new knowledge surrounding the physiological activity of tocotrienol, a natural analogue of tocopherol.

RESULTS

The biological activity of vitamin E has generally been associated with its well-defined antioxidant property, specifically against lipid peroxidation in biological membranes. In the vitamin E group, alpha-tocopherol is considered to be the most active form. However, recent research has suggested tocotrienol to be a better antioxidant. Moreover, tocotrienol has been shown to possess novel hypocholesterolemic effects together with an ability to reduce the atherogenic apolipoprotein B and lipoprotein(a) plasma levels. In addition, tocotrienol has been suggested to have an anti-thrombotic and anti-tumor effect indicating that tocotrienol may serve as an effective agent in the prevention and/or treatment of cardiovascular disease and cancer.

CONCLUSION

The physiological activities of tocotrienol suggest it to be superior than alpha-tocopherol in many situations. Hence, the role of tocotrienol in the prevention of cardiovascular disease and cancer may have significant clinical implications. Additional studies on its mechanism of action, as well as, long-term intervention studies, are needed to clarify its function. From the pharmacological point-of-view, the current formulation of vitamin E supplements, which is comprised mainly of alpha-tocopherol, may be questionable.

In vitro and in vivo effects of selenium and selenium with vitamin E on platelet functions in diabetic rats relationship to platelet sorbitol and fatty acid distribution

In vitro 30 min of incubation with selenomethionine (Sm) + vitamin E multiplied by about five platelet selenium (Se) decreased significantly platelet thrombin and ADP-induced aggregation decrease. Four groups of streptozotocin-induced diabetic rats were fed with a supplemented purified diet with an Se-rich yeast (Selenion): DSel, Sm: DSm, Sm alpha-tocopherol: DSmE or unsupplemented diet: D. After 24 wk of supplementation, only a decrease in thrombin-induced aggregation in group DSel compared to DSm and DSmE and D was observed. However, after 24 wk of diet compared to 14 wk, in group D and DSm, a significant increase in thrombin-induced aggregation occurred (p < 0.0001), whereas a significant decrease in groups DSel and DSmE (p < 0.0001, p < 0.03) was noted. After 21 wk of diet, in DSmE, platelet adhesion to fibronectin was significantly decreased compared to group D (p < 0.05). These changes in DSmE were associated with a significant decrease in platelet sorbitol (p < 0.02) and a very significant increase in platelet Se (p < 0.0005). Sm associated with vitamin E would appear more efficient to prevent oxidative damage of diabetic platelet membrane and thus to modulate its hyperactivity.

Effect of vitamin E and selenium on hypothermic restraint stress and chemically-induced ulcers

The present study was undertaken to determine the effect of a combination of selenium and vitamin E on stress and chemical-induced gastric ulcers in rats. The gastric mucosal lesions were produced by hypothermic restraint stress, indomethacin, reserpine, and mucosal damaging agents including 80% ethanol, 0.6 M HCl, 25% NaCl, and 0.2 M NaOH. The gastric secretion studies were undertaken using Shay's pylorus ligation model. The results of this study demonstrated that the treatment of rats with selenium or vitamin E significantly reduced the basal gastric acid secretions when given individually; however, the combination of these agents produced a better inhibition of gastric acid secretions as compared to their individual effect. Both selenium and vitamin E were found to protect gastric mucosa against the lesions produced by hypothermic restraint stress and chemicals, but a highly significant protection was observed when they were used concomitantly. Vitamin E alone and with selenium significantly inhibited ethanol-induced depletion of gastric nonprotein sulfhydryl compounds. Our findings also showed that the combination of selenium and vitamin E provided better protection to gastric mucosa against hypothermic restraint-induced gastric wall mucus depletion. This study clearly suggests the feasibility of using selenium and vitamin E concurrently to achieve better gastroprotective effects.

Characteristics of the protective action of alpha-Tocopherol in vascular hypoxia

The functioning of the guinea-pig isolated portal vein was monitored by measuring spontaneous mechanical activity, responses to electrical stimulation and administered noradrenaline in normoxic conditions. The effect of hypoxia, induced by bubbling the physiological bathing solution with a 95% N(2)/5% CO(2) gas mixture, on the mechanical performance of the vein was then assessed. Spontaneous activity declined in hypoxia, with mean contraction tension reduced by 55 + or - 8.8%. The responses to electrical field stimulation (2-32 Hz, 0.7 msec. 70 V) were lowered by 14 + or - 4.6% but contractions produced by a range of noradrenaline concentrations (0.01-160 mu M) were unaffected by hypoxia. Substitution of glucose in the bathing solution with sucrose, a substrate unavailable to the cells for energy generation, produced a marked enhancement of the effect of hypoxia. Spontaneous activity was reduced by 76 + or - 8.3%, electrically-induced activity by 80 + or - 14.4% and noradrenaline-induced responses by 85 + or - 6.8%. Although in normoxia the activity and responses of the portal vein were unaffected by the presence of alpha-tocopherol, it significantly protected the functioning of the vein in hypoxic conditions. This effect was concentration-dependent within the range 10-160 mu M and was most marked when glucose was replaced by sucrose in the bathing solution.

Dipyridamole attenuates the development of iminodipropionitrile-induced dyskinetic abnormalities in rats

The present investigation was undertaken to study the effect of dipyridamole on experimental dyskinesia in rats. The movement disorders were produced by intraperitoneal administration of iminodipropionitrile (IDPN) in the dose of 100 mg/kg per day for 12 days. Dipyridamole was administered orally, daily 30 min before IDPN in the doses of 0.5 g/kg, 1 g/kg, and 1.5 g/kg bodyweight in three different groups of rats. Twenty-four hours after the last dose of IDPN, animals were observed for neurobehavioral changes including vertical and horizontal head weaving, circling, backwalking, grip strength, and righting reflex. Immediately after behavioral studies brain specimens were collected for analysis of vitamin E, conjugated dienes, and lipid hydroperoxides as indices of oxygen-derived free radical (OFR) production. Our results showed that concurrent use of dipyridamole significantly protected rats against IDPN-induced neurobehavioral changes in a dose-dependent manner. Treatment of rats with dipyridamole inhibited IDPN-induced decrease of vitamin E and increase in conjugated dienes and lipid hydroperoxides in brain. These findings suggest the involvement of OFR in dipyridamole induced protection against the development of IDPN dyskinesia. Further studies are warranted to determine the role of dipyridamole as a prophylactic agent against the drug induced dyskinetic abnormalities.

Effect of selenium and vitamin E on iminodipropionitrile induced dyskinesia in rats

The present study was undertaken to determine the effect of combination of selenium and vitamin E on experimentally induced dyskinesia in rats. The dyskinetic syndrome was produced in 4 groups of 6 male rats each weighing 250-300g by intraperitoneal (ip) administration of iminodipropionitrile (IDPN) in doses of 100 mg/kg body weight daily for 12 days. A group of 6 rats (group 1) served as control and received normal saline only. The rats in group 2 (IDPN only) received normal saline (ip) 30 minutes before the administration of IDPN. The animals in groups 3, 4 and 5 received selenous acid (5 mumol/kg), vitamin E (500 mg/kg p.o.) and a combination of selenous acid and vitamin E respectively, daily, 30 minutes before IDPN for 12 days. Twenty four hours after the last dose of IDPN, the dyskinetic behavior including vertical head movements (retrocollis), horizontal head movements (laterocollis), circling and backwalking of each rat was studied for a period of 10 minutes. Immediately after behavioral studies, the animals were sacrificed and brains were dissected out for the analysis of conjugated dienes, lipid hydroperoxides and vitamin E. The results of this study showed that treatment of rats with IDPN only for 12 days produced dyskinetic syndrome in all the rats characterized by vertical and horizontal head movements, circling and backwalking. Concomitant treatment of rats with vitamin E and selenium individually reduced IDPN induced dyskinesia, and the symptoms were almost completely absent when the combination of these two agents was used.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin E: molecular and biological function

There is a growing body of evidence implicating free radicals in a wide variety of medical diseases and conditions, especially the diseases of ageing, such as cancer and cardiovascular disease, which appear to be ultimate expressions of long-term, cumulative and sustained cellular damage. Vitamin E is an excellent lipid-soluble, chain-breaking antioxidant in the presence of other co-operative antioxidants such as vitamin C or ubiquinol, but it can act as a pro-oxidant in their absence. Epidemiological findings and animal studies support the belief that vitamin E is protective against cardiovascular disease and possibly cancer. The wide range of symptoms associated with vitamin E deficiency is consistent with a loss of antioxidant protection in those long-lived cells in which there is sufficient opportunity for accumulation of free radical damage. The cellular damage is proposed to arise from the generation of free radicals during normal aerobic metabolism. Some susceptible tissues may have enhanced levels of radicals that are produced, for example, by the action of cytochrome P-450 enzymes in steroidogenic tissues, or by the generation of NO in neural tissues.