Effect of Vitamin E on Platelet Aggregation in Diabetes Mellitus

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.

Bovine retinal pericytes are resistant to glucose-induced oxidative stress in vitro

Diabetic retinopathy is a sight-threatening complication of diabetes, and loss of pericytes represents early signs of its development. We tested the hypothesis that high glucose levels may induce signs of oxidative stress in cultured bovine retinal pericytes. Pericytes were exposed to either normal (5.5 mM) or high (22 mM) glucose levels for 1, 3, and 5 days. Signs of oxidative stress were measured by expression of copper/zinc superoxide dismutase, manganese superoxide dismutase, catalase, and glutathione peroxidase using real-time RTPCR. To elucidate the role of oxidative stress, we also measured glutathione (GSH) concentration in the cells and investigated the impact of thiol-reactive metal ions and hydrogen peroxide (H(2)O(2)) on intracellular GSH. Despite the stimulation with high glucose, thiol-reactive metal ions, or H(2)O(2), there was no clear increased expression of antioxidant enzymes or influence of GSH levels. Lipid peroxidation (malondialdehyde level) was increased in bovine aortic smooth muscle cells, but not in bovine retinal pericytes. The data indicate that pericytes do not develop oxidative stress in response to hyperglycemia. However, it is not definitively excluded that oxidative stress may occur after longer time periods of glucose stimulation.

Dietary supplements: altered coagulation and effects on bruising

BACKGROUND

Patient use of dietary supplements that alter coagulation or have an effect on bruising is becoming increasingly common.

OBJECTIVE

To identify and describe dietary supplements that alter coagulation or are reported to alter bruising during and after surgical procedures.

METHODS

The MEDLINE, Cochrane Collaboration, and International Bibliographic Information on Dietary Supplements databases were searched for articles using the search words "bruising," "bleeding," "coagulation," "hemostasis," "herbal medicine," "alternative medicine," and "dietary supplement." Additional sources were obtained from manual searches of recent journal articles.

RESULTS

In vivo and in vitro evidence supports the notion that many dietary supplements alter coagulation. Limited evidence is available to support anecdotal claims of diminished postoperative bruising after the use of dietary supplements.

CONCLUSION

Surgeons should be aware that many of their patients are taking dietary supplements that may alter coagulation. Because most patients will not readily volunteer this information, specific steps should be taken to obtain it prior to more extensive surgical procedures.

Diabetic patients without vascular complications display enhanced basal platelet activation and decreased antioxidant status

Vascular complications are the leading causes of morbidity and mortality in diabetic patients. The contribution of platelets to thromboembolic complications is well documented, but their involvement in the initiation of the atherosclerotic process is of rising interest. Thus, the aim of the present study was to evaluate basal arachidonic acid metabolism in relation to the redox status of platelets in both type 1 and type 2 diabetic patients, in the absence of vascular complications, as compared with respective control subjects. For the first time, we show that basal thromboxane B(2), the stable catabolite of thromboxane A(2), significantly increased in resting platelets from both type 1 and type 2 diabetic patients (58 and 88%, respectively), whereas platelet malondialdehyde level was only higher in platelets from type 2 diabetic subjects (67%). On the other hand, both vitamin E levels and cytosolic glutathione peroxidase activities were significantly lower in platelets from diabetic patients as compared with respective control subjects. We conclude that platelet hyperactivation was detectable in well-controlled diabetic patients without complications. This abnormality was associated with increased oxidative stress and impaired antioxidant defense in particular in type 2 diabetic patients. These alterations contribute to the increased risk for occurrence of vascular diseases in such patients.

An update on the role of free radicals and antioxidant defense in human disease

Mounting clinical and experimental evidence indicates that free radicals play important roles in many physiological and pathological conditions. The wider application of free radical measurement has increased awareness of functional implications of radical-induced impairment of the oxidative/antioxidative balance. In the following review, the role of oxygen free radicals in some human and experimental pathological conditions is described, with particular emphasis on the mechanisms by which they produce oxidative damage to lipids, proteins, and nucleic bases. The role of free radicals and the activation of the antioxidant systems in arteriosclerosis and ageing, diabetes, ischemia/reperfusion injury, ethanol intoxication, and liver steatosis is discussed. Therapeutic approaches to the use of antioxidants have been described and prospects for clinical use have been considered.

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.

Surgically significant nutritional supplements

This is not an exhaustive study of all nutritional supplements that patients may be taking. The most frequently used and those potentially most detrimental or most beneficial for surgical patients have been chosen for review of pertinent effects. It is essential to ask patients specifically about supplements or unusual dietary habits that may affect their surgical outcome prior to their invasive procedure and to keep in mind the supplements that may improve their outcome.

Human fibroblast cells produce a factor that stimulates prostacyclin synthesis by vascular endothelial cells

The prostacyclin (PGI2) produced by vascular endothelium plays a key role in maintaining vascular homeostasis. The present study demonstrated that the conditioned medium (CM) of human diploid fibroblast cells contained PGI2-stimulatory activity (PSA) for bovine aortic endothelial cells (BAEC) and human umbilical vein endothelial cells (HUVEC). CM significantly stimulated the production of 6-keto-PGF1 alpha, a stable PGI2 metabolite, by both cultured BAEC and HUVEC in a concentration-dependent manner. Since the factor responsible for the PSA seemed to be negatively charged, PSA was partially purified using a DEAE-5PW high performance liquid chromatography column. The partially purified PSA was completely inhibited by preincubation with 15 microM indomethacin, a cyclooxygenase inhibitor. However, partially purified PSA was partially inhibited by preincubation with 50 microM mepacrine, a phospholipase A2 inhibitor. These findings suggest that PSA stimulates preferentially cyclooxygenase relative to phospholipase A2 in vascular endothelial cells. The partially purified PSA showed no effect on thromboxane A2 production by human washed platelets, and had no growth-promoting activity on BAEC. We conclude that cultured human fibroblast cells produce factor that stimulate the synthesis of prostaglandin by vascular endothelial cells but not by platelets.

Phospholipid fatty acid composition and vitamin E levels in the retina of obese (fa/fa) and lean (FA/FA) Zucker rats

We have compared the fatty acid composition of the major classes of phospholipids in the retina of lean (FA/FA) and genetically obese (fa/fa) male Zucker rats. In all phospholipid fractions, there was a higher ratio of n-3 to n-6 fatty acids in obese animals whereas the total content of polyunsaturated fatty acids (PUFA) was unaffected by the genotype. Lower percentages of arachidonic acid (20:4(n-6)) were present in the phosphatidylcholine, phosphatidylinositol and phosphatidylserine fractions in the retina of obese rats. This was associated with a higher level of docosahexaenoic acid (22:6(n-3)) in these fractions. In addition, increased levels of dihomo-gamma-linolenic acid (20:3(n-6)) were present in the retinal phosphatidylcholine and phosphatidylethanolamine of obese animals. These results indicate that modifications of phospholipid fatty acid composition which have previously been reported in peripheral tissues of obese Zucker rats also affect the retina. Furthermore, the retinal levels of vitamin E were higher in obese than in lean rats suggesting differences in the tissue antioxidant status between these two genotypes.

Effects of thromboxane synthetase inhibitor (OKY-046) on urinary prostaglandin excretion and renal function in streptozotocin-induced diabetic rat

The present study was undertaken to evaluate the effects of a selective thromboxane synthetase inhibitor (OKY-046) on urinary prostaglandins (PGs) excretion and renal parameters such as endogenous creatinine clearance rate (Ccr) and urinary protein excretion in streptozotocin (STZ)-induced diabetic rats. STZ-diabetic rats were divided into two groups; one fed standard chow (DM1) and the other, standard chow mixed with 0.1% OKY-046 (DM2) for 24 weeks. Male Wistar rats were fed standard chow for 24 weeks as control (C). Urinary thromboxane B2 (TXB2) and 6-keto-PGF1 alpha excretions significantly increased in STZ-induced diabetic rats (DM1 and DM2) compared with C after 24 weeks. The increased urinary TXB2 excretion in DM2 was significantly reduced (p < 0.05) compared with that in DM1 (261.1 +/- 18.6 ng/gCr versus 380.0 +/- 48.4 ng/gCr, mean +/- SEM). No significant difference could be found in urinary protein excretion between DM1 and DM2, which was significantly higher in both diabetic groups than C after 12 and 24 weeks. Ccr in both DM1 and DM2 significantly increased (p < 0.05) compared with C after 12 weeks. In contrast, after 24 weeks, Ccr in DM1 fell down to 0.18 +/- 0.02 mL/min 100 g body weight (BW), thus being significantly lower (p < 0.05) than that in C (0.27 +/- 0.03 mL/min 100 g BW) and DM2 (0.25 +/- 0.02 mL/min 100 g BW). Electron microscopic findings in diabetic rats after 24 weeks were the typical change of early diabetic nephropathy, whereas there were no obvious differences between DM1 and DM2.(ABSTRACT TRUNCATED AT 250 WORDS)

Diabetes mellitus: a disease of abnormal cellular calcium metabolism?

Although the pathogenesis of the diabetes mellitus syndrome remains poorly understood, both insulin-dependent diabetes mellitus and non-insulin-dependent diabetes mellitus predispose the individual to a similar spectrum of complications, including hypertension, macrovascular and microvascular disease, cataracts cardiomyopathy, neuropathy, and premature aging, suggesting that these complications develop along a pathway common to both diabetic conditions. Yet not all diabetic persons are affected by all of these complications or to the same degree. What causes this marked variability in the clinical manifestations of the diabetes syndrome remains an enigma. Accumulating data from animal models of diabetes and from studying patients with diabetes reveal that intracellular calcium levels are increased in most tissues. The activities of the membrane, adenosine triphosphatase (ATPase) associated cation pumps, which determine intracellular calcium level (i.e., calcium-ATPase and [sodium + potassium]-ATPase), are also altered. The nature of the alteration is often tissue specific and may depend on the level of blood glucose or insulin, or both. In this review we discuss the potential contribution of these changes in intracellular calcium regulation, whether acquired or genetically determined, to the pathogenesis of the diabetes syndrome, to the abnormalities in insulin secretion and action (mainly in non-insulin-dependent diabetes), and to the complications of both diabetes syndromes. Altered intracellular calcium metabolism may represent a common, underlying abnormality linking the metabolic, cardiovascular, ocular, and neural manifestations of the diabetic disease process.

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.

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.

Influence of antiplatelet drugs on occlusion of arteriovenous fistula in uraemic patients

A long-standing arteriovenous (A-V) fistula may develop thrombotic complications. In 20 patients on intermittent peritoneal dialysis (IPD) arteriovenous fistula was made surgically. We evaluated the efficacy of three antiplatelet drugs: Ibustrin (Group A), sulphinpyrazone (Group B) and alpha-tocopherol (Group C) in preventing thrombotic occlusion of A-V fistulas. Results of the trial indicate that the three drugs significantly reduce spontaneous platelet aggregation and ADP induced aggregation. The heparin neutralizing activity was significantly increased during treatment. Significant prolongation of bleeding time was observed only in Groups B and C. In patients receiving antiplatelet drugs no occlusion of A-V fistulas was observed. In the control group such complications occurred in 3 of the 20 patients. Our results indicate that antiplatelet drugs by inhibiting the platelet function may prevent thrombotic occlusions of A-V fistulas in IPD patients.

Increased inositol phosphate accumulation in platelets from patients with NIDDM

We evaluated thrombin-induced inositol phosphate accumulation in [3H]inositol-labeled platelets prepared from patients with non-insulin-dependent diabetes mellitus. There were no significant differences in [3H]inositol incorporation into and contents of phosphoinositides between the diabetic patients and their age-matched control subjects. Thrombin induced a dose- and time-dependent accumulation of inositol phosphate. The accumulation of [3H]inositol trisphosphate and [3H]inositol bisphosphate by thrombin stimulation were significantly enhanced in platelets from the diabetic patients, although the accumulation of [3H]inositol monophosphate did not differ between the diabetic patients and the control subjects. In addition, the platelet aggregation rate induced by thrombin was also significantly enhanced in the diabetic patients in correlation with the enhanced inositol phosphate accumulation. These results suggest that increased inositol phosphate accumulation may cause accelerated platelet functions in diabetes mellitus.

Increased intracellular calcium mobilization in platelets from patients with type 2 (non-insulin-dependent) diabetes mellitus

Enhanced platelet functions have been reported in patients with diabetes mellitus. Our recent study demonstrated that phosphoinositide turnover is increased in platelets from diabetic patients. In the present study, we evaluated the abnormality in platelet intracellular calcium mobilization in patients with Type 2 (non-insulin-dependent) diabetes mellitus using fura-2, a fluorescent calcium indicator. Washed platelets were prepared from six diabetic patients with increased platelet aggregation rates (DM-A group), seven diabetic patients with normal platelet aggregation rates (DM-B group), and eight age-matched healthy control subjects. The basal intracellular free calcium concentrations in platelets were similar among the three groups. Thrombin (0.025-0.1 U/ml) induced a dose-dependent increase in intracellular calcium in both the presence and the absence of extracellular calcium. This increase in the presence of extracellular calcium, which depends on calcium influx and release, was significantly higher in the DM-A group than in the DM-B and control groups. However, there was no significant difference between the control group and the DM-B group. In the absence of extracellular calcium, thrombin-induced calcium increase, which depends only on calcium release, was also significantly enhanced in the DM-A group. Furthermore, the calcium increase stimulated by platelet-activating factor (10 nmol/l) with and without extracellular calcium was significantly higher in the DM-A group than in the other groups. Additionally, calcium ionophore A23187 (100 nmol/l) caused a significantly higher calcium increase in the DM-A group with extracellular calcium, while the calcium increase without extracellular calcium showed no significant difference among the three groups. These observations suggest that enhanced intracellular calcium mobilization due to increased calcium influx and release may be closely related to platelet hyperfunctions in diabetes mellitus.

Oxidative status and oral contraceptive. Its relevance to platelet abnormalities and cardiovascular risk

Oral contraceptive (OC) use is a risk for thrombogenic events. This paper reviews effects of OC on oxidative status, coagulation, and platelet activity. Complicating effects of cardiovascular risk factors such as smoking, diabetes, hyperpidemia, and hypertension, are discussed. From these data we conclude that: 1. OC use modifies slightly but significantly the oxidative status in women and in animals by decreasing in plasma and blood cells the antioxidant defenses (vitamins and enzymes). 2. The changes in the oxidative status are related to an increase in plasma lipid peroxides apparently responsible for the hyperaggregability and possibly the imbalance in clotting factors associated with the OC-induced prethrombotic state. 3. These effects of OC appear to be increased by a high intake of polyunsaturated fat and counteracted by supplements of vitamin E. 4. The risk factors acting synergistically with OC, have all been shown to increase platelet reactivity. In addition, smoking, diabetes, and, to some extent, dyslipidemia are associated with an increased level of lipid peroxides and concomitant changes in the antioxidant defenses that can be additive to those induced by OC. Thus, free radicals and lipid peroxidation could be the underlying mechanism in the predisposition to thrombosis induced by most risk factors in OC users. 5. Results of epidemiologic and experimental studies in this field will be concordant only when diet and natural antioxidants will be systematically taken into consideration.

Reduction of urinary albumin excretion by thromboxane synthetase inhibitor, OKY-046, through modulating renal prostaglandins in patients with diabetic nephropathy

We evaluated the effects of thromboxane synthetase inhibitor, OKY-046, on urinary albumin and prostaglandin (PG) excretion in 14 patients with non-insulin-dependent diabetes mellitus (NIDDM). Urinary excretion of 6-keto-PGF1 alpha (a stable metabolite of PGI2), TXB2 (a stable metabolite of TXA2) and PGE2 in NIDDM patients was comparable with that in control subjects. However, the urinary 6-keto-PGF1 alpha/TXB2 ratio in NIDDM patients with both micro- and macroalbuminuria was significantly (P less than 0.001) lower than that in the controls. By a single administration of OKY-046 (40 mg, i.v.) to the diabetic patients, urinary TXB2 excretion significantly (P less than 0.05) decreased from 169.7 +/- 23.9 to 140.2 +/- 17.9 ng/gCr, but urinary 6-keto-PGF1 alpha and PGE2 excretion did not change significantly. The urinary 6-keto-PGF1 alpha/TXB2 ratio thus significantly (P less than 0.01) increased from 1.02 +/- 0.13 to 1.73 +/- 0.41 as associated with significant increments in urine volume (P less than 0.05), urinary sodium excretion (P less than 0.01) and creatinine clearance (P less than 0.05). Of 14 diabetic patients, 7 with macroalbuminuria (albumin index exceeding 100 mg/gCr) were orally given OKY-046 (600 mg/day) for 8 weeks. After this period, the urinary albumin index significantly (P less than 0.05) decreased from 524.9 +/- 149.6 to 317.6 +/- 90.6 mg/gCr.(ABSTRACT TRUNCATED AT 250 WORDS)

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

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

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.

Functions and tocopherol content of blood platelets from elderly people after low intake of purified eicosapentaenoic acid

Elderly people present an increased incidence of atherosclerosis and vascular cerebral damages, associated with blood platelet hyperactivity and a stimulation of arachidonic acid metabolism in vivo. The effects of a low intake of purified eicosapentaenoic acid (EPA) on platelet hyperactivity in old human subjects has been investigated. In a randomized, double blind study, 8 people took during 2 months a daily intake of 100 mg of eicosapentaenoic acid (EPA) given as a triglyceride (1,3-dioctanoyl,2-eicosapentaenoyl-glycerol), and 8 other subjects ingested a placebo. A slight, but significant reduction of platelet-rich plasma aggregation in response to epinephrine and arachidonic acid occurred after EPA intake, as well as a decreased aggregation of washed platelets induced by thrombin, although collagen- and U-46619-induced aggregations were not significantly modified. EPA intake failed to affect arachidonic acid metabolism in thrombin-stimulated platelets or in clotted venous blood. The urinary excretion of thromboxane, 6-keto-PGF1 alpha and their 2,3-dinor-metabolites was also not modified. Similarly, no change in the plasma and platelet lipid fatty acid compositions could be observed. Platelet, but not plasma, alpha- and gamma-tocopherol were enhanced by EPA intake. An increase of platelet vitamin E has been associated with a decrease of aggregation, especially in vitamin E-deficient subjects, like elderly people. Therefore, low intake of EPA might have contributed to inhibit platelet aggregation by increasing cellular vitamin E.

Effects of small concentrations of eicosapentaenoic acid on platelets

Increased platelet functions have been associated with enhanced arachidonic acid (AA) metabolism in diabetics and elderly people. We investigated these parameters in both groups after feeding low doses of pure eicosapentaenoic acid (EPA). After such an intake, platelet aggregation induced by various agonists was decreased whereas the oxygenated metabolism of endogenous AA was not substantially altered, and the fatty acid composition of plasma and platelet lipid pools did not change. In the most recent study, the measurement of vitamin E revealed that although its level in plasma was not modified, it was increased in platelets after EPA intake. It is concluded that small amounts of EPA intake do not reduce platelet aggregation in competing with AA metabolism but rather in depressing the peroxide tone of the cell.

Abnormality in prostacyclin-stimulatory activity in sera from diabetics

A reduction in prostacyclin (PGI2) production by vascular wall may cause platelet hyperaggregability in diabetics, which is considered to be a possible pathogenesis of diabetic vascular complications. In the present study, the presence of PGI2-stimulatory activity (PSA) in rat and human plasma-derived serum (PDS) was confirmed by cultured bovine aortic endothelial cells. PSA in PDS was significantly decreased in streptozotocin-induced diabetic rats and in patients with non-insulin-dependent diabetes mellitus (NIDDM). PDS from patients with NIDDM showed less PSA prior to the clinical onset of diabetic vascular complications, such as retinopathy and proteinuria. The reduction in PSA was still observed in dialyzed PDS from the patients with NIDDM. The nondialyzable PSA was heat-stable at 56 degrees C for 30 minutes and partially stable at 100 degrees C for five minutes. This activity was not extractable with diethylether and was precipitable with trichloroacetic acid. The study of Sephadex G-50 column chromatography showed that a major part of PSA in dialyzed PDS was found in the area of the molecular weight of 12,000 to 17,000 daltons. In conclusion, the reduction in PSA from diabetics may cause a reduction of PGI2 production by vascular wall, subsequently contributing to the development of diabetic vascular complications.

Vitamin E fails to alter the aggregation and the oxygenated metabolism of arachidonic acid in normal human platelets

Using low doses of vitamin E, either in vitro or in vivo, we have succeeded in almost doubling plasma and platelet alpha-tocopherol in healthy humans. Despite such an enrichment, platelet aggregation induced by collagen and thromboxane A2 minetic U46619 was not much affected, although that induced by exogenous arachidonic acid was significantly decreased. Similarly, the oxygenation of exogenous arachidonic acid was not modified. When incubated with thrombin some variations in the formation of endogenous cyclooxygenase and lipoxygenase products could be observed, although rarely significantly. The tendency was a decrease after in vivo enrichment and an increase when enrichment occurred in vivo. Serum oxygenated metabolites of arachidonic acid as well as urinary metabolites of thromboxane and prostacyclin were also not affected after vitamin E supplementation. Since the lipoxygenation of eicosapentaenoic acid was very strongly peroxide-dependent, the effect of alpha-tocopherol enrichment was tested and the 12-hydroperoxide derivative of arachidonic acid was used as a physiological peroxide. No modification could be observed, confirming that vitamin E does not alter the specific peroxidation of polyunsaturated fatty acids in normal platelets. We conclude that vitamin E supplementation neither affects arachidonic acid-dependent aggregation nor the oxygenated metabolism of arachidonic acid in normal human platelets.

Platelets and aging. I--Aggregation, arachidonate metabolism and antioxidant status

Platelet functions were investigated in sixteen old (78-94 years) and eight young (25-35 years) subjects. Whole blood platelet aggregation induced by collagen was higher in the elderly. Similarly, aggregation of platelet rich plasma and plasma-free platelets induced by various agents was increased but the collagen-induced release of ATP was reduced. In agreement with the enhanced platelet aggregability, the increase of thromboxane formation (under thrombin stimulation) was also noted in platelets from elderly people. To further assess platelet and vascular function in vivo, we measured the excretion of urinary TXB2, 2,3-dinor TXB2, 6-keto-PGF1 alpha and 2,3-dinor-6-keto-PGF1 alpha. The four metabolites were all increased in the elder population. In addition, a significant reduction of platelet vitamin E was observed in the elderly people, although the plasma content was normal. These results indicate numerous modifications of platelet behaviour with aging. They include the increased platelet susceptibility to aggregation, and the depletion of ATP granule content, which could reflect an activation in vivo in agreement with the enhanced urinary excretion of thromboxane and prostacyclin metabolites. We hypothesize that platelet hyperactivity associated with the enhanced oxygenated metabolism of arachidonic acid could be linked to vitamin E depletion. These changes may reveal a prethrombotic state in the elderly population.

Effects of vitamin E therapy on ethanol-induced changes in platelet aggregation, thromboxane formation, factor VIII levels and serum lipids

A transient increase in platelet thromboxane formation has been observed in non-alcoholics during acute ethanol intoxication and in alcoholics shortly after ethanol withdrawal. Whether these effects are related to the generation of free radicals and lipid peroxidation was investigated by using vitamin E as a free radical scavenger and inhibitor of lipid peroxide formation. The results demonstrate that a high dose of vitamin E (1800 IU) taken daily by non-alcoholic men slightly (P less than 0.05) decreases aggregation-associated platelet thromboxane formation during ethanol oxidation. Likewise, vitamin E prevents the ethanol-induced increase (P less than 0.01) in factor VIII coagulant activity. These observations suggest that the enhancement of platelet thromboxane formation and factor VIII coagulant activity by acute ethanol ingestion may be related to stimulated lipid peroxidation. By contrast, similar effects of vitamin E were not found in alcoholics shortly after ethanol withdrawal suggesting other mechanisms for their platelet hyperreactivity.

Effects of linoleic acid and gamma-linolenic acid intake on platelet functions in elderly people

Sixteen old subjects were given daily dietary supplement of lg of linoleic acid and lg of gamma-linolenic acid (primerose oil) or 2g of linoleic acid (sunflower oil) for periods of two months. Haemostatic parameters, platelet aggregation, exogenous and endogenous arachidonic acid metabolism were investigated before and after the intake. Diets did not induce any significant change in haemostatic parameters (bleeding time, levels of anti-thrombin III, plasminogen and plasma beta-TG and PF4). Platelet rich plasma aggregation induced by collagen and arachidonic acid were significantly reduced after linoleic acid (18:2n-6) intake. In contrast, gamma-linolenic acid (18:3n-6) supplement did not alter aggregation. However, thromboxane B2 formation (under stimulation) and vitamin E level in platelets (but not in plasma) were decreased after 18:3n-6 as compared to 18:2n-6 intake. The mechanism of thromboxane B2 decrease is unclear. Nevertheless, we may speculate that beneficial effect of this decrease could be counterbalanced by the decreased platelet vitamin E. We conclude that intake of 18:2n-6 or 18:3n-6 does not affect much platelet functions in elderly people.

Abnormalities of platelet function in hypertension and diabetes

The increased frequency of hypertension in diabetes and of abnormalities of carbohydrate metabolism in hypertension are now well established. It is conceivable that the high coincidence of the two diseases is based on a common metabolic defect. Studies of platelets permit the evaluation of the stimulatory, phosphoinositol-linked and the inhibitory, cyclic adenosine 3',5'-monophosphate-dependent pathways of cell activation. Furthermore, platelets may be relevant for the development of angiopathy through their contents of growth factors. Abnormalities of platelet aggregation have been demonstrated in hypertension and diabetes. They are accompanied by exaggerated stimulation of adenylate cyclase in hypertension and abnormal activity of cyclic guanosine 3',5'-monophosphate phosphodiesterase in diabetes. Defective function of platelets is also observed in patients and animals when the two diseases are present at the same time. Both increased and decreased aggregation have been described in these two diseases in the literature. The apparent discrepancies may be due to different types of platelet preparation, evaluation of aggregation, evolution of defect with age, and form of the disease. Integrated studies of biochemical mechanisms responsible for cell activation are needed to characterize the exact defect present in diabetes and hypertension in platelets.