Enhanced collagen-induced responses of platelets from rabbits with diet-induced hypercholesterolemia are due to increased sensitivity to TxA2. Response inhibition by chronic ethanol administration in hypercholesterolemia is due to reduced TxA2 formation

Korean red ginseng attenuates hypercholesterolemia-enhanced platelet aggregation through suppression of diacylglycerol liberation in high-cholesterol-diet-fed rabbits

Intake of Korean red ginseng (KRG, ginseng Radix rubra), rich in glycosylated saponins (ginsenosides), has been known to inhibit platelet aggregation in the normocholesterolemic condition. However, it is unclear whether KRG can attenuate hypercholesterolemia-enhanced platelet aggregation. This study examined whether the daily consumption of a KRG-water extract (WE) could prevent the hypercholesterolemia-enhanced platelet aggregation and progression of hypercholesterolemic atherosclerosis. KRG-WE administration (200 mg/kg/day) for 8 weeks potently inhibited the platelet aggregation induced by low doses of agonists (0.5 microg/mL collagen and 0.025 unit/mL thrombin), whereas it weakly reduced the blood-cholesterol levels and formation of atheromatous lesions. In further investigation, KRG-WE significantly suppressed collagen-induced 1,2-diacylglycerol liberation, but had no significant effect on arachidonic acid liberation. Taken together, it can be suggested that the antiplatelet effect of KRG-WE may, at least partly, be due to the inhibition of 1,2-diacylglycerol generation rather than regulation of blood lipid levels. In conclusion, daily consumption of KRG-WE could be a useful alternative measure for the prevention of thrombus and atheroma formation in hypercholesterolemia.

Enhanced release of sphingosine-1-phosphate from hypercholesterolemic platelets: role in development of hypercholesterolemic atherosclerosis

Although it is well known that sphingosine-1-phosphate (S1P), which induces many biological responses, is present in plasma and is mainly released from activated platelets, little is known whether the release of S1P is increased when platelets are activated in the hypercholesterolemic condition, and what are the roles of increased S1P generation in the development or progression of the atherosclerosis. Results show that 0.5% cholesterol diet for 16 weeks induces platelet hyperaggregability to low doses of agonists as well as development of hypercholesterolemic atherosclerosis in the rabbits. The generation and released level of S1P were significantly increased in the hypersensitized platelets and blood plasma in hypercholesterolemic rabbits. We also demonstrated that S1P increased VSMC proliferation via endothelial differentiation gene (EDG)-1 receptor dependent pathway. Our results indicate that release of S1P from activated platelets was increased by enhanced platelet sensitivity in hypercholesterolemia, which potentiated the ox-LDL-induced VSMC proliferation via EDG-1 receptor pathway.

Effects of alcohol on hemostasis

Several epidemiologic studies have shown that moderate intake of alcohol is associated with a lower risk of cardiovascular disease (CVD), but the mechanism is not fully elucidated. One of the proposed mechanisms of the protective effect of moderate alcohol intake is its beneficial effect on hemostasis. The aim of this review is to summarize the effect of ethanol intake on platelet aggregation and activation, coagulation factors including von Willebrand factor (vWF), and the fibrinolytic system. With regard to the effect of alcohol on platelet function, evidence in the literature suggests both platelet activation and platelet inhibition by ethanol. A unifying hypothesis is that platelets are partially activated by ethanol, with partial degranulation allowing for continued circulation of platelets with impaired function. Evidence also exists showing that ethanol intake decreases fibrinogen, factor VII, and vWF levels. In addition, alcohol intake has been found to increase fibrinolysis by increasing tissue plasminogen activator activity. The effect of ethanol on platelets, coagulation factors, and the fibrinolytic system is likely to contribute to protection against CVD.

Effects of alcohol on platelet functions

Recent epidemiologic studies have consistently shown that moderate intake of alcoholic beverages protect against morbidity and mortality from coronary heart disease and ischemic stroke. By contrast, alcohol drinking may also predispose to cerebral hemorrhage. These observations suggest an effect of alcohol similar to that of aspirin. Several studies in humans and animals have shown that the immediate effect of alcohol, either added in vitro to platelets or 10 to 20 min after ingestion, is to decrease platelet aggregation in response to most agonists (thrombin, ADP, epinephrine, collagen). Several hours later, as, in free-living populations deprived of drinking since the previous day it is mostly secondary aggregation to ADP and epinephrine and aggregation to collagen that are still inhibited in alcohol drinkers. By contrast, in binge drinkers or in alcoholics after alcohol withdrawal, response to aggregation, especially that induced by thrombin, is markedly increased. This rebound phenomenon, easily reproduced in rats, may explain ischemic strokes or sudden death known to occur after episodes of drunkenness. The platelet rebound effect of alcohol drinking was not observed with moderate red wine consumption in man. The protection afforded by wine has been recently duplicated in rats by grape tannins added to alcohol. This protection was associated with a decrease in the level of conjugated dienes, the first step in lipid peroxidation. In other words, wine drinking does not seem to be associated with the increased peroxidation usually observed with spirit drinking. Although further studies are required, the platelet rebound effect of alcohol drinking could be associated with an excess of lipid peroxides known to increase platelet reactivity, especially to thrombin.

Wines and grape juices as modulators of platelet aggregation in healthy human subjects

To test the hypothesis that red wine, by virtue of its relatively high concentration of polyphenols, is more protective against atherosclerosis and coronary heart disease (CHD) than white wine, and that grape juice enriched in one of these, trans-resveratrol, may share some of these properties, studies were performed on 24 healthy males aged 26-45 years. Each consumed the following beverages for periods of 4 weeks: red wine, white wine, commercial grape juice and the same grape juice enriched with trans-resveratrol. Apart from the last beverage, 2 weeks abstinence was maintained before commencing the schedule. Blood was taken at the beginning and end of each schedule to determine plasma thromboxane B2 (TxB2) concentration and the IC50 (concentration required for 50% aggregation) for ADP and thrombin-induced platelet aggregation. White wine (P < 0.05) but not red wine increased the IC50 for ADP. Both wines increased the IC50 for thrombin (P < 0.02 and P < 0.001, respectively) and also lowered plasma TxB2 concentrations (P < 0.01 and P < 0.025, respectively). Neither grape juice altered ADP-induced aggregation or TxB2 concentrations, but the commercial juice lowered the IC50 for thrombin (P < 0.001) whereas the resveratrol-enriched juice caused a dramatic increase (P < 0.001). In vitro experiments demonstrated that the aggregation of fresh washed human platelets by ADP and thrombin was moderately reduced by both grape juices, strongly by red wine and not at all by white wine. The synthesis of TxB2 by platelets from labelled arachidonate was stimulated by commercial grape juice, slightly enhanced by resveratrol-enriched juice and strongly inhibited by red wine with white wine having little effect. Platelets from subjects consuming the commercial juice had a higher ratio of cyclo-oxygenase to lipoxygenase product formation and those consuming the resveratrol-enriched juice a lower ratio than during the control period. We conclude that trans-resveratrol can be absorbed from grape juice in biologically active quantities and in amounts that are likely to cause reduction in the risk of atherosclerosis. The failure of red wines (which have a 20-fold excess of polyphenols over white wines) to show any advantage suggests that, in vivo, ethanol is the dominant anti-aggregatory component in these beverages which are more potent than grape juices in preventing platelet aggregation in humans.

Effects of dietary fatty acids on signal transduction and membrane cholesterol content in rat platelets

Previously, we have reported that dietary fatty acids can modify the thromboxane A2-dependent activation of rat platelets. Here, we present evidence that this dietary effect is part of a more general effect on platelet signal transduction, putatively involving structural changes in the platelet membranes. Four experiments were performed, where Wistar rats were fed with a high-fat diet enriched in either saturated, n-6 polyunsaturated or n-3 polyunsaturated fatty acids, or with a low-fat diet enriched in n-6 polyunsaturated fatty acids. The type of diet hardly influenced mean number of double bonds in the major platelet phospholipids. Platelet membranes from the rats fed with the saturated-fat diet had phospholipids with relatively high levels of arachidonate, but were low in cholesterol/phospholipid ratio. When compared to this diet group, platelets from other groups had an arachidonate content that was 21 to 47% lower and a cholesterol/phospholipid ratio 3 to 5% higher. The saturated-fat diet resulted in platelets that, in general, were less responsive to agonists than the platelets from other groups: with thrombin, collagen and thromboxane A2 analogue U46619, both early (shape change and phospholipase C-dependent rise in [Ca2+]i) and late (exocytosis and aggregation) responses were relatively low. However, platelet activation evoked by ADP was not influenced by diet type. When the cholesterol content of rat platelets was modified in vitro, it appeared that the early and late responses to thrombin and U46619 increased with the cholesterol/phospholipid ratio. Taken together, these results suggest that in rat platelets (i) the membrane cholesterol/phospholipid ratio can be modulated by a diet rich in saturated fatty acids, explaining, at least in part, the dietary effect on phospholipase C-mediated platelet activation, and (ii) relatively small changes in cholesterol content can have a more profound effect on platelet activation than substantial changes in arachidonate level.