Modulation of Platelet thromboxane A2 and arterial prostacyclin by dietary vitamin E

Platelet Oxidative Stress and its Relationship with Cardiovascular Diseases in Type 2 Diabetes Mellitus Patients

Enhanced platelet activation and thrombosis are linked to various cardiovascular diseases (CVD). Among other mechanisms, oxidative stress seems to play a pivotal role in platelet hyperactivity. Indeed, upon stimulation by physiological agonists, human platelets generate and release several types of reactive oxygen species (ROS) such as O2 -, H2O2 or OH-, further amplifying the platelet activation response via various signalling pathways, including, formation of isoprostanes, Ca2+ mobilization and NO inactivation. Furthermore, excessive platelet ROS generation, incorporation of free radicals from environment and/or depletion of antioxidants induce pro-oxidant, pro-inflammatory and platelet hyperaggregability effects, leading to the incidence of cardiovascular events. Here, we review the current knowledge regarding the effect of oxidative stress on platelet signaling pathways and its implication in CVD such as type 2 diabetes mellitus. We also summarize the role of natural antioxidants included in vegetables, fruits and medicinal herbs in reducing platelet function via an oxidative stress-mediated mechanism.

Effects of vitamin E on the response of the fetal middle cerebral artery to the pressure test

OBJECTIVE

To examine the effects of the maternal administration of vitamin E on the vasoreactivity of the middle cerebral artery (MCA) in preterm fetuses.

STUDY DESIGN

The vasoconstrictive response of the proximal segment of the MCA to brief and partial external occlusions of the umbilical vein (pressure test) was studied in 22 fetuses between 21 and 35 weeks of gestation, before, and 3 to 7 days after, the maternal administration of oral vitamin E (50 mg daily).

RESULTS

The vasoconstrictive activity of the MCA was eliminated in 15 fetuses (68.2%), unchanged in six (27.3%), and decreased in one (4.5%). In the latter seven cases, vasoconstriction of the proximal MCA in response to the pressure test was eliminated by increasing the vitamin E dosage to 100 mg/day.

CONCLUSION

Vitamin E administered to the mothers had a pronounced effect on the proximal MCA reactivity in preterm fetuses.

Vitamin E increases production of vasodilator prostanoids in human aortic endothelial cells through opposing effects on cyclooxygenase-2 and phospholipase A2

Impairment of endothelium-dependent vasodilation is associated with the initiation and development of atherosclerosis. Vasodilator prostanoids constitute a protective mechanism in maintaining normal vasomotor function. In the current study, we determined the effect of in vitro vitamin E supplementation at physiologically relevant concentrations (10-60 micromol/L) on the production of the vasodilator prostanoids prostaglandin I(2) (PGI(2); prostacyclin) and prostaglandin E(2)(PGE(2)) by human aortic endothelial cells (HAECs) as well as its underlying mechanism. Results showed that vitamin E dose dependently (10-40 micromol/L) increased the production of both prostanoids by HAECs. This was associated with a dose-dependent (10-40 micromol/L) upregulation of cytosolic phospholipase A(2) (cPLA(2)) expression and arachidonic acid release. In contrast, vitamin E dose dependently (10-60 micromol/L) inhibited cyclooxygenase (COX) activity but did not affect the expression of either COX-1 or COX-2, indicating that the effect of vitamin E on COX activity was post-translational. Thus, vitamin E had opposing effects on the 2 key enzymes in prostanoid biosynthesis; at the concentrations used in this study, this resulted in a net increase in the production of vasodilator prostanoids. The vitamin E-induced increase in PGI(2) and PGE(2) production may contribute to its suggested beneficial effect in preserving endothelial function.

Atorvastatin reduces the plasma lipids and oxidative stress but did not reverse the inhibition of prostacyclin generation by aortas in streptozotocin diabetic rats

The effect of atorvastatin (Lipitor) on diabetes-induced changes in plasma lipids, oxidative stress and the ability of aortic tissues to generate prostacyclin was studied in streptozotocin diabetic rats. In diabetic rats, plasma total cholesterol, triglycerides and serum glucose significantly increased compared to nondiabetic rats. Atorvastatin administration to diabetic rats did not affect hyperglycemia but significantly reduced plasma total cholesterol and triglycerides compared to diabetic rats. The oxidative stress markers urinary isoprostane, liver thiobarbituric acid reactive substances (TBARS) and plasma protein carbonyl content significantly increased in diabetic rats compared to nondiabetic rats. Atorvastatin admnistration to diabetic rats significantly reduced oxidative stress levels compared to diabetic rats, but urinary isoprostane and liver TBARS remained significantly higher than nondiabetic rats. Prostacyclin (PGI(2)) generation by aortic tissues significantly decreased in diabetic rats compared to nondiabetic rats. Atorvastatin administration to diabetic rats did not reverse that inhibition. These results were discussed in the light of the possible effects of hyperglycemia and statins on NAD(P)H-oxidase and cyclooxygenase-2 activities and the genetic difference between rats and other mammals regarding the level of vascular superoxide dismutase (SOD) activity.

Vitamin C or Vitamin B6 supplementation prevent the oxidative stress and decrease of prostacyclin generation in homocysteinemic rats

We hypothesize that homocysteinemia causes oxidative stress, decreases the aortic ability to generate prostacyclin and that antioxidants have a protective role. Four groups of eight rats each were fed for 8 weeks the control diet (group A), control diet with folic acid omitted and excess methionine (Me) added to drinking water (group B), diet B + 500 mg/kg of Vitamin C (group C) or diet B + 60 mg/kg Vitamin B6 (group D). The three groups of rats fed folic acid deficient (FD) diets (groups B, C and D) were homocysteinemic as indicated by the significant increase in their serum homocysteine (HC) concentration. Rats fed diet B had oxidative stress as indicated by an increase in serum thiobarbituric acid reactive substances (TBARS) and advanced oxidation protein products (AOPP) and urinary isoprostanes and had a decreased ability of their aortas to generate prostacyclin. Homocysteinemic rats fed a FD diet + Vitamin C (group C) or Vitamin B6 (group D) also had high levels of serum homocysteine but the oxidative stress markers and the ability of their aortas to generate prostacyclin returned to normal. This indicates that the homocysteinemic effect is through an oxidative mechanism and that Vitamin C as a free radical scavenger prevents these effects. Serum Vitamin C and liver glutathione concentrations significantly increased in rats fed excess Vitamin B6 compared to the control or FD rats. This may explain why Vitamin B6 has an antioxidative effect.

High density lipoprotein can modulate the inhibitory effect of oxLDL on prostacyclin generation by rat aorta in vitro

To examine the effect of oxidized low density lipoprotein (oxLDL) on prostacyclin (PGI2) generation by rat aorta in vitro and whether high density lipoprotein (HDL) has any protective effect against the inhibition of PGI2 generation induced by oxLDL is the objective of this study. Preincubation of aortas with oxLDL resulted in significant inhibition of PGI2 generation compared to preincubation with normal low density lipoprotein (nLDL) or buffer only. The inhibitory effect of oxLDL resided in its lipid moiety while the lipid fraction of nLDL showed no effect. Aortas preincubated with 10 microg/ml of lyso phosphatidycholine (lyso PC) also showed 30% inhibition of PGI2 generation, indicating that lyso PC was among the lipid components of oxLDL which inhibited PGI2 generation. Preincubation of aortas with a mixture of HDL and oxLDL at a ratio of 10:1 showed a significant recovery of PGI2 generation compared to aortas preincubated with only oxLDL, indicating a protective role for HDL. When HDL was incubated with oxLDL the transfer of lyso PC from oxLDL to HDL suggested that HDL trapped lyso PC from oxLDL thus preventing it from acting on the aorta. However, when a mixture of HDL and oxLDL at a ratio of 3:1 was preincubated with aortas, no protective effect of HDL was observed. Preincubation of aortas with a mixture of HDL plus oxLDL at a ratio of 8:1, which was incubated for 1 h at 37 degrees C, produced significantly less PGI2 than aortas preincubated only with oxLDL, indicating that HDL under these conditions was not protective but even enhanced the inhibitory effect of oxLDL. Similarly, aortas preincubated with HDL plus whole oxLDL (at a ratio of 10:1); containing all the small molecular weight oxidation products and characterized by high levels of thiobarbituric acid reactive substance (TBARS) and lipid hydroperoxides; produced significantly less PGI2 than aortas preincubated with whole oxLDL. These results were evaluated in light of possible modification of HDL by oxLDL and its lipid oxidation products such as aldehydes and lipid peroxides. The modified HDL can add more lipid peroxides and increase the effectiveness of lipid peroxides originally present in oxLDL.

Plasma levels of antioxidant vitamins C and E are decreased in vascular parkinsonism

Oxidative stress is an important mechanism of cell death in Parkinson's disease (PD) and brain ischemia. Vitamins C, E and A are important antioxidants and deficiency of these agents has been implicated in the mechanisms of atherosclerosis. We measured the levels of the above antioxidant vitamins in 44 patients with PD, 12 patients with vascular parkinsonism (VP), 11 patients with other parkinsonism syndromes of various causes and 39 controls. Vitamin A levels did not differ between groups. Vitamins C and E were found decreased in VP, while they were normal in PD indicating low levels of antioxidant vitamins in VP and stressing the necessity of maintaining sufficient dietary intake of these agents in the elderly.

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.

Comparison of antioxidant effects of naringin and probucol in cholesterol-fed rabbits

BACKGROUND

Due to the strong evidence on the involvement of active oxygen species in a variety of disorders, the role of antioxidants against oxidative stress has recently received increased attention.

METHODS

Twenty male rabbits were served a high-cholesterol (HC, 5 g/kg diet) diet or high-cholesterol diet supplemented with naringin (0.5 g/kg diet) or probucol (0.5 g/kg diet) for 8 weeks to compare the antioxidative effects of the citrus bioflavonoid (naringin) and antioxidative cholesterol-lowering drug (probucol).

RESULTS

The plasma thiobarbituric acid-reactive substances (TBARS) concentration was not significantly different between the groups, whereas the hepatic TBARS concentration was significantly lower in the probucol group than in both normal and HC control or naringin group. Probucol and naringin supplementation led to an increase in the hepatic superoxide dismutase (SOD) and catalase (CAT) activities, and a decrease in the hepatic mitochondrial hydrogen peroxide (H(2)O(2)) content compared to the HC-control group. However, there was no difference in the cytosolic H(2)O(2) content or cytosolic glutathion peroxidase (GSH-Px) activity in the liver between the groups. Both naringin and probucol supplements significantly increased the plasma vitamin E concentration compared to the HC-control group. As regards the antioxidant enzyme gene expressions, naringin significantly increased the expression of three antioxidant enzyme mRNAs compared to the HC-control group, whereas probucol significantly increased the only SOD mRNA expression.

CONCLUSIONS

The probucol supplement was very potent in the antioxidative defense system, whereas naringin exhibited a comparable antioxidant capacity based on increasing the gene expressions in the antioxidant enzymes, while also increasing the hepatic SOD and CAT activities, sparing plasma vitamin E, and decreasing the hepatic mitochondrial H(2)O(2) content.

Oxidized low density lipoprotein inhibits prostacyclin generation by rat aorta in vitro: a key role of lysolecithin

The objective of this study was to examine the effect of oxLDL on prostacyclin (PGI2) generation by rat aortic segments and to see whether the lipid fraction of oxLDL or its components are responsible for that effect. We also tested if antioxidants have any protective role. LDL oxidized by copper was characterized by higher TBARS, conjugated diene, lysophosphatidylcholine (lyso PC), oxysterols and less polyunsaturated fatty acids (PUFA) than nLDL. Preincubation of aortas with oxLDL caused a significant inhibition of PGI2 generation compared to aortas preincubated with nLDL or buffer only. The percent inhibition was dependent on the concentration of oxLDL. Most of the inhibitory effect of oxLDL resided in its lipid moiety while the lipid fraction of nLDL, as well as native LDL had no effect. Preincubation of aortas with 10 microg/ml of 7-ketocholesterol the major oxysterol in oxLDL reduced the amount of PGI2 generated by aorta at all times tested; however that decrease did not reach a significant level. Aortas preincubated with 10 microg/ml of lyso PC showed a 21-36% inhibition of PGI2 generation which was comparable to the inhibition produced by preincubating the aortas with 50 microg protein/ml of oxLDL (containing about 7.5 microg lyso PC). This indicated that most of the inhibitory effect of oxLDL was due to its lyso PC. The small molecular weight fraction (< 10 kDa) with a high level of TBARS (TBARS solution) also significantly decreased the PGI2 generation by aorta. Addition of superoxide dismutase (SOD) + catalase or vitamin E simultaneously with oxLDL or TBARS solution in the preincubation medium did not reverse their inhibitory effects. This indicated that oxygen free radicals are not a contributing factor to the inhibitory effect of oxLDL but lyso PC and the lipid peroxides and probably other components already present within oxLDL are the important inhibitors.

Oxidized low-density lipoprotein (LDL) enhances thromboxane A(2) synthesis by platelets, but lysolecithin as a product of LDL oxidation has an inhibitory effect

Oxidation of low-density lipoprotein (LDL) by copper sulfate led to a significant increase in lysophosphatidylcholine (lyso PC) at the expense of phosphatidylcholine. Incubation of different concentrations of oxidized LDL (oxLDL) (32-650 microg protein/ml) with platelets for 1 h at 37 degrees C increased lyso PC content. The increase was dependent on oxLDL concentration. Incubation of platelets with various concentrations of lyso PC in solution for 5 or 15 min showed that lyso PC percentage was increased in the platelet membrane and the increase was dose dependent. Platelets incubated with various concentrations of lyso PC (2-100 microM) for 5 or 15 min and then triggered with thrombin also showed a significant decrease of thromboxane A(2) (TXA(2)) release as lyso PC concentration reached 10 microM or 6 microM, respectively. The decrease of TXA(2) release was more significant as lyso PC concentration was increased. The present study showed that this inhibition of TXA(2) release by lyso PC was due to 1) inhibition of phospholipase A(2) and the decrease of free arachidonic acid liberation from platelet phospholipid and 2) inhibition of cyclooxygenase. These inhibitory effects of lyso PC were discussed in relation to its effect on membrane fluidity. Lyso PC at concentrations of 30, 50, and 100 microM caused a sudden drop in TXA(2) release and a sudden increase of lactic dehydrogenase loss from the platelets due to their lysis and inhibition of cyclooxygenase enzyme. The present study shows that oxLDL contains high levels of lyso PC that are transferable to the platelets and can weaken their responsiveness to thrombin and decrease TXA(2) release. In our previous study, we found that oxLDL also contained high levels of oxysterols and thiobarbituric acid reactive substances (TBARS), which enhanced platelet reactivity to thrombin and increased TXA(2) release. We conclude that the net effect of oxLDL on platelets will depend on its degree of oxidation and the ratio between oxysterols plus TBARS/lyso PC. Variations in this ratio may explain some of the contradictions cited in the literature concerning the effect of oxLDL on platelet activation.

Effect of antioxidant vitamin E as a protective factor in experimental atherosclerosis in rhesus monkeys

Atherosclerosis has been known for many years, yet its etiology remains unknown. Hypercholesterolemia is a major risk factor for atherosclerosis. The mechanism by which it triggers endothelial injury is not known. Since the role of the antioxidant vitamin E on experimental atherosclerosis is inconsistent, the present study was undertaken to evaluate platelet lipid peroxidation and the role of vitamin E (alpha-tocopherol) as protective factor in atherosclerosis in rhesus monkeys. A significant decrease in serum cholesterol and serum triglyceride levels was found in the group of animals which were reverted to stock diet along with vitamin E injections after 9 months of atherogenic diet feeding. Decreases in malonyldialdehyde levels and antioxidant enzyme activities were less significant in animals continued on an atherogenic diet feeding along with vitamin E as compared with animals fed a stock diet with vitamin E supplementation. The overall observations in this study suggest that antioxidant status and lipid peroxidation could be partly restored with vitamin E supplementation in experimental atherosclerosis. Damage to endothelial cells destroys their antithrombotic status and leads to fatal thrombosis. alpha-Tocopherol offers the best hope, but the question is how much of it should be administered for the prevention of atherosclerosis.

Hydrogenated fat high in trans monoenes with an adequate level of linoleic acid has no effect on prostaglandin synthesis in rats

Our study was designed to determine whether hydrogenated fat high in trans monoenes concentration affected prostaglandin synthesis. Corn oil (CO), butter (B), hydrogenated vegetable oil (HF) and coating fat (CF) were used in this study. These fats were fed to rats for 10 wk at 10 g/100 g diet. The phospholipid (PL) fatty acid content of platelets, aorta and heart was determined by gas liquid chromatography, and the in vitro aorta production of prostacyclin (PGI2) from exogenous or endogenous arachidonic acid (AA) was measured using the radioimmuno-assay (RIA) method. Serum thromboxane B2 (TXB2) released by platelets as thromboxane A2 (TXA2) during incubation of whole blood was also measured by this method. In the group fed CF, AA was significantly lower in the PL of aorta, platelet and heart, and the ratio 20:3(n-9)/20:4(n-6) was greater than in the groups fed CO, B or HF, indicating that the group fed CF was essential fatty acid (EFA) deficient. Although AA was significantly lower in the aorta and platelet PL of the group fed HF compared to the group fed CO, that difference did not affect the amounts of PGI2 or TXB2 produced in these groups. The group fed CF had significantly less PGI2 and TXB2 released by aorta and platelets than the other groups. This was the result of the reduced level of AA and the presence of higher amounts of 20:3(n-9) acid in the PL, which might act as a competitive inhibitor for cyclooxygenase. The aortic production of PGI2 from exogenous AA did not differ among the groups indicating that prostaglandin synthetase was not affected by the dietary fat. We conclude that the consumption of hydrogenated fats high in trans 18:1 acids with adequate amount of linoleic acid had no effect on the amount of thromboxane or prostacyclin produced by platelet or aorta in vitro.

Oxysterols and TBARS are among the LDL oxidation products which enhance thromboxane A2 synthesis by platelets

In this study, we compared the effects of normal LDL (nLDL) and oxidized LDL (oxLDL) on thromboxane (TXA2) release by platelets triggered by low concentration of thrombin, and we determined which component of oxLDL is responsible for that activation. After oxidation of LDL with copper sulfate, the small molecular weight fraction (< 10 kDa) which was high in TBARS was removed; using Amicon Centriprep-10 concentrator membrane. More than 67% of TBARS in the oxLDL preparation was found in solution while the remaining was covalently attached to the oxLDL particles. OxLDL contained significantly higher levels of oxysterols and TBARS than the nLDL. Platelets preincubated with low concentrations of oxLDL (33-132 micrograms protein/mL) produced significantly higher TXA2 than platelets preincubated with equivalent concentrations of nLDL when triggered with thrombin. Platelets treated with oxLDL also contained significantly higher levels of oxysterols than platelets treated with nLDL. Platelets preincubated with pure cholestanetriol (10 micrograms/mL) contained a high level of cholestanetriol in the membrane, and TXA2 release was significantly increased in these platelets compared to the control platelets. The TBARS in solution also was very potent in enhancing TXA2 release by thrombin-treated platelets. These results indicate that oxysterols and the free TBARS either in solution or covalently attached to the oxLDL particles are partly responsible for the stimulatory effect of oxLDL on TXA2 release by platelets. The present study also showed that this enhancement of TXA2 release was due to activation of phospholipase A2 and to the increase of arachidonic acid liberation from the platelet phospholipids.

Neurological recovery in diabetic rats following spinal cord injury

This study was designed to assess the effect of spinal cord injury on neurobehavioral, electrophysiological, structural, and biochemical changes in normal and diabetic rats. Experimental diabetes was induced in Sprague-Dawley male rats (weighing 250-280 g) with streptozotocin (50 mg/kg i.p.). Eight weeks after the treatment with streptozotocin the animals were anaesthetized with chloral hydrate and laminectomy was performed at T 7-8 level leaving the dura intact. A compression plate (2.2 x 5.0 mm) loaded with a weight of 35 g was placed on the exposed spinal cord for 5 min. Postoperative neurological function was assessed using inclined plane test, modified Tarlov score, and vocal and sensory score daily for 10 days. Electrophysiological changes were assessed using somatosensory and corticomotor evoked-potentials. The animals were sacrificed at different time intervals and injured site of the spinal cord was analyzed for changes in vitamin E and glutathione levels (as markers of oxidative stress). Pathological changes in spinal cord were also studied using light microscopy. The data on neurobehavioral study clearly indicated that the compression of spinal cord produced highly significant neurological deficit and poor recovery in diabetic rats as compared to nondiabetic rats. Our histopathological and electrophysiological results also confirmed that diabetic animals are more susceptible to compressive spinal cord injury as compared to nondiabetic animals. A higher depletion of antioxidant defense markers (vitamin E and glutathione) was observed in diabetic rats as compared to nondiabetic rats. These results point toward the role of free radicals in poor recovery in diabetic rats following neurotrauma. Further studies are warranted to assess the neuroprotective potential of antioxidants to retard the secondary pathophysiological events following neurotrauma and to enhance the recovery.

Glucosamine may retard atherogenesis by promoting endothelial production of heparan sulfate proteoglycans

Heparan sulfate proteoglycans produced by vascular endothelium may function physiologically to restrain the migration, multiplication, and phenotypic transition of vascular smooth-muscle cells, and to maintain an anticoagulant luminal surface by bonding and activating antithrombin III. Thus, ample production of heparan sulfate proteoglycans may act to prevent atherosclerosis and its thrombotic complications. The ability of exogenous heparin to stimulate synthesis of heparan sulfate proteoglycans by vascular endothelium may be largely responsible for the positive outcomes of most controlled evaluations of low-dose heparin as a long-term therapy for coronary disease. Glucosamine, a biosynthetic precursor of mucopolysaccharides, can substantially enhance mucopolysaccharide production when added to cultured fibroblasts or chondrocytes; the clinical utility of oral glucosamine in osteoarthritis may reflect increased synthesis of cartilage proteoglycans. It is reasonable to speculate that exogenous glucosamine will likewise enhance heparan sulfate proteoglycans production by vascular endothelial cells, and, when administered orally in regimens comparable to those effective in osteoarthritis, will thereby act to retard atherogenesis.

Oxygen free radicals and platelet activation

This article reviews our current understanding of the role of oxygen free radicals in platelet activation. Several studies have indicated that platelets, in analogy to other circulating blood cells, are able to produce oxygen free radicals, which are likely to play an important role in the mechanism of platelet activation and aggregation. Platelet activation has been obtained with very low, physiologically relevant concentrations of radicals generated chemically, by leukocytes, and by hemoglobin derived from membrane leakage of erythrocytes. Knowledge of the role of reactive species in platelet physiology is relevant because platelets are brought into close contact with other cells capable of producing free radicals, such as neutrophils, macrophages, and endothelial cells, during the formation of thrombus. The physiopatological importance of these findings is high because it is now emerging that free radicals may have a role in the mechanism of atherosclerosis and its thrombotic complications, where the causative role of platelets is well documented. This background suggests therapeutic interventions with antioxidants as antiplatelet agents to improve the pharmacological effect of classical antiplatelet drug such as aspirin.

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.

Possible mechanisms for the protective action of alpha-tocopherol in vascular hypoxia

1. The mechanism of the protective action of alpha-tocopherol (vitamin E) in sustaining noradrenaline-induced responses in vascular hypoxia was investigated using pharmacological methods. 2. Four vascular spasmogenic agents, methoxamine, acetylcholine, histamine and potassium, each with a different mode of action were used to produce responses in guinea-pig isolated portal vein. In each case the responses were significantly reduced by hypoxia or hypoxia and a substrate-free environment. 3. Pre-incubation of the vein with alpha-tocopherol protected the noradrenaline-induced responses against hypoxia in the substrate-free environment, However, at the EC50 concentration for protection of noradrenaline, alpha-tocopherol failed to protect the responses of each agent from the inhibitory effects of hypoxia, suggesting a mechanism of protection involving noradrenaline. 4. Drugs known to interfere with the disposition of noradrenaline in sympathetically innervated tissues, cocaine, hydrocortisone and tyramine did not affect the response to alpha-tocopherol. 5. Responses to calcium were unaffected by alpha-tocopherol in normoxia and hypoxia. 6. The protective action of alpha-tocopherol was not mimicked by the chromanol ring of the vitamin structure, Trolox C, suggesting that the vascular protection in hypoxia was not dependent on an antioxidant mechanism. 7. However, the glycolytic enzyme inhibitor, iodoacetic acid, prevented the protective action of the vitamin in hypoxia, suggesting that alpha-tocopherol enhanced noradrenaline-mediated activity in hypoxia through an iodoacetic acid-sensitive pathway.

Up-regulation of intracellular signalling pathways may play a central pathogenic role in hypertension, atherogenesis, insulin resistance, and cancer promotion--the 'PKC syndrome'

The modern diet is greatly different from that of our paleolithic forebears' in a number of respects. There is reason to believe that many of these dietary shifts can up-regulate intracellular signalling pathways mediated by free intracellular calcium and protein kinase C, particularly in vascular smooth muscle cells; this disorder of intracellular regulation is given the name 'PKC syndrome'. PKC syndrome may entail either a constitutive activation of these pathways, or a sensitization to activation by various agonists. The modern dietary perturbations which tend to induce PKC syndrome may include increased dietary fat and sodium, and decreased intakes of omega-3 fats, potassium, calcium, magnesium and chromium. Insulin resistance may be both a cause and effect of PKC syndrome, and weight reduction and aerobic training should act to combat this disorder. PKC syndrome sensitizes vascular smooth muscle cells to both vasoconstrictors and growth factors, and thus promotes both hypertension and atherogenesis. In platelets, it induces hyperaggregability, while in the microvasculature it may be a mediator of diabetic microangiopathy. In vascular endothelium, intimal macrophages, and hepatocytes, increased protein kinase C activity can be expected to increase cardiovascular risk. Up-regulation of protein kinase C in stem cells may also play a role in the promotion of 'Western' fat-related cancers. Practical guidelines for combatting PKC syndrome are suggested.

Lipid peroxidation, prostacyclin and thromboxane A2 in pigs depleted of vitamin E and selenium and supplemented with linseed oil

In a 2 x 2 balanced factorial experiment the biochemical effects on pigs of two dietary factors were investigated. The first factor was alpha-tocopherol and Se supplementation and the second factor was supplementation with alpha-tocopherol-stripped linseed oil. In pigs fed on diets depleted of alpha-tocopherol and Se, increases in concentrations of markers of lipid peroxidation (4-hydroxynonenal and hexanal) were observed. However, skeletal myopathy was only observed in those pigs fed on diets depleted of alpha-tocopherol and Se and supplemented with oil. In those pigs, increased lipid peroxidation was observed in heart and supraspinatus muscle. The plasma concentration of thromboxane B2 was increased in pigs fed on diets depleted of alpha-tocopherol and Se, suggesting an increased tendency towards platelet aggregation. However, this change was reversed in pigs depleted of alpha-tocopherol and Se, but supplemented with oil. This may have been a consequence of loss of arachidonic acid, the substrate for thromboxane formation, as a result of 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.

Inhibition of platelet aggregation and eicosanoid production by phenolic components of olive oil

This study was designed to investigate the in vitro effects of phenolic compounds extracted from olive oil and from olive derived fractions. More specifically, we investigated the effects on platelets of 2-(3,4-di-hydroxyphenyl)-ethanol (DHPE), a phenol component of extra-virgin olive oil with potent antioxidant properties. The following variables were studied: aggregation of platelet rich plasma (PRP) induced by ADP or collagen, and thromboxane B2 production by collagen or thrombin-stimulated PRP. In addition, thromboxane B2 and 12-hydroxyeicosatetraenoic acid (12-HETE) produced during blood clotting were measured in serum. Preincubation of PRP with DHPE for at least 10 min resulted in maximal inhibition of the various measured variables. The IC50s (concentration resulting in 50% inhibition) of DHPE for ADP or collagen-induced PRP aggregations were 23 and 67 microM, respectively. At 400 microM DHPE, a concentration which completely inhibited collagen-induced PRP aggregation, TxB2 production by collagen- or thrombin-stimulated PRP was inhibited by over 80 percent. At the same DHPE concentration, the accumulation of TxB2 and 12-HETE in serum was reduced by over 90 and 50 percent, respectively. We also tested the effects of PRP aggregation of oleuropein, another typical olive oil phenol, and of selected flavnoids (luteolin, apigenin, quercetin) and found them to be much less active. On the other hand a partially characterized phenol-enriched extract obtained from aqueous waste from olive oil showed rather potent activities. Our results are the first evidence that components of the phenolic fraction of olive oil can inhibit platelet function and eicosanoid formation in vitro, and that other, partially characterized, olive derivatives share these biological activities.

Increased susceptibility to lipid oxidation of low-density lipoproteins and erythrocyte membranes from diabetic patients

The aim of the present study was to determine if low-density lipoproteins (LDLs) and red blood cell (RBC) membranes from diabetic patients present an increased susceptibility to lipoperoxidation, which might be related to the increased incidence of atherosclerosis in diabetes. LDLs and RBC membranes were isolated from 11 insulin-dependent (IDDM) and 18 non-insulin-dependent diabetic (NIDDM) patients and exposed to a peroxidative stress by incubation with phenylhydrazine. The susceptibility to peroxidation was determined by measuring the production of thiobarbituric acid-reactive substances (TBARS) after the incubation. The following parameters were also evaluated: plasma glucose, triglycerides (TG), phospholipids (PL), total and high-density lipoprotein (HDL) cholesterol, apolipoprotein (apo) A-I, apo B, hemoglobin A1c (HbA1c), LDL PL and cholesterol, LDL fatty acid composition, and RBC membrane PL and cholesterol. Although they were apparently normolipidemic, diabetic patients showed an increased susceptibility to peroxidation in LDLs and erythrocyte membranes as compared with control subjects. The amount of arachidonic acid in LDLs and the PL concentration of RBC membranes from diabetic patients were significantly higher than in normal subjects. The increased lipoperoxidability of both RBC membranes and LDLs might play a central role in the pathogenesis of the vascular complications of diabetes mellitus.

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)

Coagulation activation in diabetes mellitus: the role of hyperglycaemia and therapeutic prospects

Numerous studies have shown that coagulation abnormalities occur in the course of diabetes mellitus, resulting in a state of thrombophilia. These observations are supported by epidemiological studies which demonstrate that thromboembolic events are more likely to occur in diabetic patients. The coagulation abnormalities observed in diabetic patients seem to be caused by the hyperglycaemia, which also constitutes the distinguishing feature of this disease. These data are also supported by in vitro studies which demonstrate how glucose can directly determine alterations in the coagulation system. The abnormalities observed involve all stages of coagulation, affecting both thrombus formation and its inhibition, fibrinolysis, platelet and endothelial function. The final result is an imbalance between thrombus formation and dissolution, favouring the former. Hyperglycaemia probably determines the onset of these abnormalities through three mechanisms which are, respectively, non-enzymatic glycation, the development of increased oxidative stress and a decrease in the levels of heparan sulphate. The first seems to affect the functionality of key molecules of coagulation in a negative sense. Oxidative stress constitutes an important pro-thrombotic stimulus, while the decrease in heparan sulphate determines a reduction in antithrombotic defenses. Good metabolic control could play a key role in controlling the coagulation irregularities in diabetes. However, considering the difficulties in achieving such an objective, it is possible that the use of drugs may represent a valid alternative. In fact, several drugs exist which are of potential interest. It is, however, necessary to perform long-term studies which demonstrate unequivocably that by controlling the coagulation abnormalities in diabetic patients, prolongation of life is possible.

Ischemia: reperfusion injury and restenosis after coronary angioplasty

Percutaneous transluminal coronary angioplasty (PTCA) is a very effective technology that allows, without surgery, successful mechanical revascularization of acutely or chronically obstructed coronary arteries. The success of PTCA in patients with acute myocardial infarction or unstable angina is questioned by early coronary reocclusion and by so-called reperfusion injury. In a biochemical context, reperfusion injury occurs as a very complex interaction between the different tissues that build heart muscle. Free radicals play a pivotal role and initiate a deleterious cascade of events after reperfusion. Protective mechanisms such as superoxide dismutase, glutathione peroxidase, and catalase are normally present in the cell to prevent damage by free radicals. Endothelial cells have a greater number of specific physiologic and metabolic functions and influence the microcirculatory flow. In the presence of exogenous glucose, coronary endothelial cells show a pronounced lactate production under well-oxygenated conditions. Low energy demand and high glycolytic activity may be the cause of why the coronary endothelium is less severely injured than the cardiomyocytes in the ischemic and anoxic heart. The success of PTCA in patients with chronically obstructed coronary arteries (stable angina) is questioned by vessel occlusion and restenosis. Restenosis is a very complex process involving clinical, morphological, procedural, regional flow-dependent, and biological determinants. Early platelet deposition, formation of mural thrombus, coronary vasospasm, and elastic recoil forces of stretched vessel wall may contribute to early restenosis in the first days after PTCA, but the peak incidence of restenosis occurs between two and three months after PTCA. Intimal hyperplasia or proliferation of smooth muscle cells is believed to be the fundamental process of restenosis. To solve the problem of restenosis, much effort has been expended, which includes several technical and pharmacological approaches. Pharmacological strategies, systemically or locally administered, aim at increased vasomotor tone, platelet function, smooth muscle cell proliferation/migration, and fibrocollagenous healing. Up to now none of the proposed drugs has been able to reduce the restenosis rate. There is experimental evidence for a claim that the antioxidant functions of vitamins (E, C, and beta-carotene) may prevent restenosis post-PTCA. Until recently, in most post-PTCA restenosis trials the angiographic analyses were not performed using computerized measurement methods. In order to assess the efficacy of acute or long-term interventions on the natural course or acute complications of coronary artery disease, quantitative measures have been introduced and validated that make use of digital coronary angiography and computerized image processing techniques.(ABSTRACT TRUNCATED AT 400 WORDS)

Vitamin E restores reduced prostacyclin synthesis in aortic endothelial cells cultured with a high concentration of glucose

Reduced prostacyclin (PGI2) production by the vascular wall may play an important role in the pathogenesis of vascular lesions such as atherosclerosis. The present study was undertaken to evaluate the effect of vitamin E on the production of PGI2 and other prostaglandins (prostaglandin E2 [PGE2], thromboxane A2 [TXA2], and 15-hydroxyeicosatetraenoic acid [15-HETE]) by bovine aortic endothelial cells cultured in a high concentration of glucose (300 mg/dL). Compared with endothelial cells cultured in 100 mg/dL glucose, the production of PGI2 and other prostaglandins, except 15-HETE, was significantly reduced in cultures containing 300 mg/dL glucose when stimulated by histamine, the Ca2+ ionophore, A23187, or human plasma-derived serum (PDS). The addition of vitamin E to each stimulant significantly restored the production of PGI2, PGE2, and TXA2, products of the cyclo-oxygenase pathway, in aortic endothelial cells cultured in 300 mg/dL glucose. This effect of vitamin E on the stimulation of prostaglandin production was generally specific for D-alpha-tocopherol, but not for the other vitamin E analogs tested. However, vitamin E and the stimulants had no effect on the production of 15-HETE, a product of the lipoxygenase pathway. Moreover, vitamin E alone, without stimulants, did not affect prostaglandin production in cultured bovine aortic endothelial cells. These results suggest that vitamin E may restore reduced PGI2, PGE2, or TXA2 production by bovine aortic endothelial cells cultured in a high concentration of glucose. It seems likely that vitamin E may restore depressed PGI2 production by the vascular wall in hyperglycemic conditions such as those seen in patients with diabetes mellitus.

Modulation of the platelet thromboxane A2 and aortic prostacyclin synthesis by dietary selenium and vitamin E

Vitamin E and selenium (Se) interact synergistically as an important antioxidant defense mechanisms. Se, an essential component of glutathione peroxidase (GSH-Px) and vitamin E decompose fatty acid hydroperoxides and hydrogen peroxides generated by free radical reactions. Vitamin E and GSH-Px may modulate arachidonic acid metabolism and the activity of cyclooxygenase enzymes by affecting peroxide concentration. The balance between arterial wall prostacyclin (PGI2) production and platelet thromboxane (TX)A2 directly influences platelet activity. In order to elucidate the differential role of dietary vitamin E and Se in aortic PGI2 and platelet TXA2 synthesis, 1-mo-old F344 rats were fed semipurified diets containing different levels of vitamin E (0, 30, 200 ppm) and Se (0, 0.1, 0.2 ppm) for 2 mo. Thromboxane B2 (TXB2) and 6-keto-PGF1 alpha, were measured by radioimmunoassay (RIA) after incubation of whole blood and aortic rings at 37 degrees C for 10 and 30 min, respectively. Vitamin E deficiency reduced plasma vitamin E to 5-17% of control-fed rats, and supplementation in vitamin E-supplemented animals increased plasma GSH-Px by 17%, compared to vitamin E-deficient rats. Se and vitamin E supplementation did not have a similar effect on TXB2 and PGI2 synthesis. Se deficiency did not alter platelet TXB2 synthesis, but significantly decreased aortic PGI2 synthesis. It was necessary to supplement with both antioxidants in order to increase PGI2 synthesis. Se and vitamin E deficient groups had a higher TXB2/PGI2 ratio (0.17 +/- 0.08) compared to Se- and vitamin E-supplemented groups (0.03 +/- 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Vitamin E supplementation, plasma lipids and incidence of restenosis after percutaneous transluminal coronary angioplasty (PTCA)

To test whether alpha-tocopherol prevents restenosis following percutaneous transluminal coronary angioplasty (PTCA), we enrolled patients in a double-blind, placebo-controlled trial. Patients were randomized after successful PTCA to receive vitamin E in the form of dl-alpha-tocopherol, 1200 IU/day, orally vs an inactive placebo for 4 months. Patients' blood was analyzed at baseline and at 4 months post-PTCA for differences in plasma lipids, lipoproteins, apolipoproteins, alpha-tocopherol, retinol, beta-carotene and lipoperoxide concentrations. One hundred patients completed the protocol. No significant difference was found in any parameter except alpha-tocopherol level between the vitamin E group and the placebo group, verifying compliance. Follow-up cardiac catheterization was obtained in 83% of the patients receiving placebo and in 86% of the patients receiving dl-alpha-tocopherol. Including thallium and exercise stress testing, objective information was obtained for practically all the patients receiving dl-alpha-tocopherol or placebo. Restenosis was defined as the presence of a lesion with greater than or equal to 50% stenosis in a previously dilated artery segment and results were analyzed with respect to pre- and post-PTCA artery diameter, vessel diameter at follow-up, and restenosis rate. Patients receiving dl-alpha-tocopherol had a 35.5% restenosis angiographically documented vs 47.5% restenosis in patients receiving the placebo. The overall incidence of restenosis defined by an abnormal angiogram or thallium test or exercise stress test was 34.6% in patients receiving dl-alpha-tocopherol and 50% in patients receiving the placebo. This difference (p = 0.06) did not reach significance because of an inadequate sample size.

Phospholipases in biology and medicine

Phospholipases, a group of enzymes that catalyze the hydrolysis of membrane phospholipids, are classified according to the bond cleaved in a phospholipid into PLA1 (EC 3.1.1.3), PLA2 (EC 3.1.1.4), PLB (EC 3.1.1.5), PLC (EC 3.1.4.3), and PLD (EC 3.1.4.4). This paper reviews source and structure of PLA2 and the involvement of PLA2 and PLC in several biological phenomena, such as, signal transduction, photoreception, biosynthesis of lung surfactant, sperm motility, and fertilization. New assays for PLA2 activity and concentration in biological fluids are discussed. Phospholipases are involved in many inflammatory reactions by making arachidonate available for eicosanoid biosynthesis. The determination of PLA2 activity and mass concentration in plasma is useful in the diagnosis and prognosis of pancreatitis and of septic shock. Naturally occurring phospholipase inhibitors, such as lipocortins act as second messengers in the anti-inflammatory response to steroids. Lipocortins may be valuable therapeutic agents, because they are more specific in their anti-inflammatory action than glucocorticoids; therefore, they are less likely to produce harmful side effects.

R,R,R-alpha-tocopherol potentiates prostacyclin release in human endothelial cells. Evidence for structural specificity of the tocopherol molecule

Human umbilical vein endothelial cells (HUVEC) in culture synthesize prostacyclin (PGI2) as the predominant metabolite of arachidonic acid which is derived from the deacylation of phospholipids. Under basal-unstimulated condition, PGI2 release from HUVEC is extremely low; however, when endothelial monolayers were preincubated with the natural vitamin E (R,R,R-alpha-tocopherol), we found a dose-dependent potentiation of basal PGI2 release. When HUVEC were stimulated with arachidonate or ionophore A23187, there was a dose-dependent increase of PGI2 release in response to tocopherol enrichment. When HUVEC were labelled with [Me-3H]choline followed by A23187 stimulation, a significantly higher lysophosphatidylcholine was found in the tocopherol-enriched cells, suggesting a change in enzymes involved in phosphatidylcholine metabolism. Analysis of these enzymes revealed that phospholipase A2 activity was enhanced by tocopherol enrichment, whereas lysophospholipase and acyl-CoA acyltransferase were unaffected. To determine the specificity of the tocopherol molecule, different analogues were tested for their PGI2 potentiating activity. Results showed that the free hydroxyl group on the chromanol ring as well as the phytyl side-chain are absolutely required to stimulate PGI2 release, whereas, different methyl locations and substituents on the chromanol ring had no effect. These studies demonstrated that tocopherol potentiates basal PGI2 release in HUVEC and in contrast to its reported inhibitory role in rat platelets, myocardium and neutrophils, tocopherol stimulates phospholipase activity in HUVEC.

The uptake of (R,R,R)alpha-tocopherol by human endothelial cells in culture

Endothelial cells from human umbilical cord vein in culture incorporate physiological and pharmacological amounts of (R,R,R)alpha-tocopherol in a time-dependent and dose-dependent manner. Incorporated tocopherol was found to associate predominantly with membrane fractions of the cell. When expressed on the basis of organelle protein, the highest amount of tocopherol was found in plasma membrane, and decreasing amounts in mitochondria, endoplasmic reticulum and cytosol. With the relatively wide range of tocopherol concentrations used in these studies (23.2-92.8 microM), there was no apparent toxicity on the cells as judged by unaltered cell numbers and cell viability. When the cells were enriched with tocopherol and cell tocopherol levels were monitored in tocopherol-free medium, there was a rapid phase of tocopherol disappearance, which was followed by a slower phase. The half-time for the disappearance of incorporated tocopherol was found to be approximately 65 +/- 8.6 hr (mean +/- SD, n = 3). The results of this study clearly show that human endothelial cells in culture are a feasible model for the study of vitamin E uptake. The cell culture model could potentially be used to study other fat-soluble vitamins and essential nutrients.

Effects of dietary vitamin E on the biosynthesis of 5-lipoxygenase products by rat polymorphonuclear leukocytes (PMNL)

Activation of polymorphonuclear neutrophils (PMNL) leads to the release of arachidonate from cellular phospholipids via a phospholipase A2, and conversion of products of the 5-lipoxygenase pathway. Evidence to date indicates the dietary vitamin E ((R,R,R)-alpha-tocopherol) can influence both cyclooxygenase and phospholipase A2 activities and that the effect of this vitamin is cell/tissue specific. The present study was undertaken in order to examine the effects of varying dietary tocopherol on PMNL tocopherol content and 5-lipoxygenase product profile using the ionophore A23187 as stimulant in the presence and absence of exogenous arachidonate. Feeding semi-purified diets containing 0, 30 or 3000 ppm of (R,R,R)-alpha-tocopherol acetate to weanling rats for 17 weeks resulted in a dose-related enrichment of PMNL tocopherol. Stimulation of PMNL elicited a significant and rapid loss of tocopherol. When PMNL were stimulated with A23187 alone, the synthesis of 5-HETE, LTB4 and 19-hydroxy-LTB4 was decreased in proportion to increasing dietary tocopherol concentrations. However, when exogenous arachidonate was provided with A23187, intermediate amounts of dietary tocopherol (30 ppm) still suppressed the formation of 5-lipoxygenase products, but high doses (3000 ppm) did not have any additional inhibitory effect. This differential response to high concentrations of vitamin E in the presence and absence of exogenous arachidonate highly suggest that at these concentrations, tocopherol may act principally at the level of substrate release whereas at lower concentrations, 5-lipoxygenase is inhibited. Data from this study demonstrated that attenuation of the formation of 5-lipoxygenase products in PMNL can be achieved by dietary vitamin E enrichment.

Lipid peroxidation in pregnancy: new perspectives on preeclampsia

Basic research during the past two decades has led to increased awareness of the role of lipid peroxidation in various physiologic and pathophysiologic processes. A number of reports indicate that preeclampsia is associated with elevated blood levels of lipid peroxidation products. In view of its potentially destructive character, uncontrolled lipid peroxidation has been suggested as an etiologic factor in preeclampsia. The present article summarizes current information regarding the occurrence of lipid peroxidation in normal and preeclamptic pregnancy. Recent progress concerning our understanding of the process of lipid peroxidation and its role in cardiovascular disease is also reviewed. This information is used to discuss potential mechanisms by which lipid peroxidation might contribute to the pathogenesis of preeclampsia.

Potentiation of atherosclerotic lesions in rabbits by a high dietary level of vitamin E

1. Two experiments were conducted to determine whether or not high dietary levels of vitamin E affect the development of atherosclerotic lesions in aortas of cholesterol-fed (5 g/kg diet) rabbits that were mechanically deendothelialized by balloon catheterization. 2. In the first experiment, the aortas of rabbits fed 2000 mg vitamin E/kg diet (i.e. 50-fold their nutritional requirement) for 8 weeks showed no gross morphological differences, either within or outside experimentally damaged areas, from those of rabbits fed the nutritionally adequate control level (40 mg/kg) of the vitamin. 3. In the second experiment, rabbits fed 10,000 mg vitamin E/kg diet (i.e. 250-fold requirement) for 14-15 weeks showed significantly greater endothelial loss and plaque formation at aortic sites outside of the mechanically damaged area than did controls. Plasma cholesterol levels were very high (9000-14,000 mg/l) and were not affected by dietary vitamin E level until 10-12 weeks when they were reduced moderately (18%). 4. It is concluded that very high levels of vitamin E can potentiate spontaneous atherosclerotic lesions, and it is suggested that this effect may depend on high cholesterol status.

Vitamin E. deficiency increases the synthesis of platelet-activating factor (PAF) in rat polymorphonuclear leucocytes

Vitamin E deficiency was found to stimulate FMLP (N-formyl-L-methionyl-L-leucyl-L-phenylalanine)-induced biosynthesis of PAF (1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine) in polymorphonuclear leucocytes (PMN) from rat peritoneum. In three separate experiments each, the amounts of PAF synthesized during 6 min and 12 min incubation of PMN cells from control, vitamin E-supplemented, and vitamin E-deficient rats were 129-240, 131-227 and 248-354 pmol/10(6) cells, respectively. The activity of the acetyl-transferase, which transfers the acetyl moiety of [3H]acetyl-CoA to 2-lysoPAF (1-O-alkyl-sn-glycero-3-phosphocholine) to form [3H]PAF, was higher in PMN homogenates from vitamin E-deficient rats (2.28 +/- 0.07 nmol/min/mg protein) than in those from E-supplemented rats (1.06 +/- 0.10 nmol/min/mg protein). However, there was no difference between the two groups in the activity of acetylhydrolase (4.26 +/- 0.71 and 4.26 +/- 0.06 nmol/min/mg protein, respectively), measured as degradation of [3H]PAF to [3H]lysoPAF. In vitro addition of alpha-tocopherol did not inhibit the increased activity of acetyl-transferase in vitamin E-deficient rats, indicating that the enzyme in vitamin E-supplemented rats was not directly inhibited by alpha-tocopherol. The acetyl-transferases of the two groups showed similar Km values for acetyl-CoA, but different Vmax values (225 microM and 6.4 nmol/min/mg protein in vitamin E-deficient rats, and 216 microM and 3.6 nmol/min/mg protein in vitamin E-supplemented rats), suggesting that the enzyme was not activated but increased in amount in vitamin E deficiency.

Protective effect of vitamin E on spinal cord injury by compression and concurrent lipid peroxidation

Studies were made on the influence of vitamin E on the effects of compression injury of the spinal cord associated with ischemia in rats. The motor disturbance induced by spinal cord injury was greatly reduced by vitamin E supplementation. After injury, the spinal cord evoked potentials showed greater recovery of both amplitude and latency in the vitamin E-supplemented group than in the control group. Spinal cord blood flow was promptly restored and remained normal after injury in the vitamin E-supplemented group, but was significantly decreased from 3 h after injury in the control group. Thiobarbituric acid (TBA)--reactive substances in the spinal cord was immediately increased by compression injury in both groups, and after injury it persisted at a high value for 24 h in the control group, but decreased within 1 h in the vitamin E-supplemented group. Pathological examination of the spinal cord showed less damage, such as bleeding and edema, in the vitamin E-supplemented group than in the control group. Vitamin E may have protective effects on the spinal cord by inhibiting damage induced by lipid peroxidation and/or by sustaining the blood flow by maintaining the normal metabolism of arachidonic acid.

Effect of vitamin E enrichment on arachidonic acid release and cellular phospholipids in cultured human endothelial cells

The effect of (R,R,R)-alpha-tocopherol on agonist-stimulated arachidonate release and cellular lipids was investigated in cultured human umbilical cord endothelial cells. Endothelial cells in culture incorporate added tocopherol in a dose-dependent manner at both physiological (23.2 microM) or pharmacological (92.8 microM) concentrations which were well tolerated by the cells, as judged by unaltered cell number and viability. Two experiments were conducted in which cells were either incubated with (R,R,R)-alpha-tocopherol followed by labelling with [1-14C]arachidonic acid or they were labelled with arachidonate followed by incubation with tocopherol. Irrespective of the sequence of incubation with arachidonate and tocopherol, (R,R,R)-alpha-tocopherol-enriched cells released significantly more labelled arachidonate when stimulated with thrombin (2.5 U/ml) or ionophore A23187 (1 microM) for 10 min. The magnitude of [1-14C]arachidonate release was higher from ionophore A23187 stimulation than from thrombin stimulation, but the trend of increased arachidonate release in tocopherol-enriched cells was the same. Results from these studies demonstrate that (R,R,R)-alpha-tocopherol can stimulate arachidonate release in human endothelial cells. This observation is in direct contrast to the role of tocopherol, which has been shown to inhibit platelet and cardiac phospholipase A2 activity in rats, and to reduce thrombin-stimulated thromboxane release in rat platelets.