Alterations in intracellular calcium homeostasis and platelet aggregation induced by ethanol

[Effect of ethanol on platelet biology]

In recent years, interest in the study of platelets, significantly increased due to recent discoveries providing convincing evidence that their functions by are not limited to their participation in the blood coagulation mechanism. Many works are devoted to the study of the functional state of platelets under conditions of acute and chronic alcohol exposure. The results of such studies can be useful for the development of new markers of the degree of alcohol intoxication of the body for the subsequent choice of the method drug correction of disorders caused by acute or chronic alcohol effects. The review summarizes results in vivo and in vitro of studies performed during more than 60 years on the effect of ethanol on the biogenesis, number, morphology and biochemistry of platelets.

Effects of ethanol on aggregation, serotonin release, and amyloid precursor protein processing in rat and human platelets

It is known that oxidative stress leads to amyloid precursor protein (APP) dysregulation in platelets. Ethanol (EtOH) is a vascular risk factor and induces oxidative stress. The aim of the present study was thus to investigate whether EtOH affects APP processing in rat and human platelets. Platelets were exposed to 50 mM EtOH with and without 2 mM calcium-chloride (CaCl₂) for 20 or 180 minutes at 37°C. Platelet aggregation, serotonin release and APP isoforms 130 and 106/110 kDa were analyzed. As a control, 100 mM H₂O₂ was tested in rat platelets. Our data show that EtOH alone did not affect any of the analyzed parameters, whereas CaCl₂ significantly increased aggregation of rat and human platelets. In addition, CaCl₂ alone enhanced serotonin release in rat platelets. EtOH counteracted CaCl₂-induced aggregation and serotonin release. In the presence of CaCl₂, EtOH reduced the 130 kDa APP isoform in rat and human platelets. In conclusion, this study shows that in the presence of CaCl₂, EtOH affects the platelet function and APP processing in rat and human platelets.

Thrombin-stimulated discharge of calcium stores in human platelets: analysis of experimental data

The purpose of this research was to analyze experimental data concerning thrombin-stimulated discharge of calcium stores in human platelets contained in calcium-free medium in view of better understanding the mechanisms involved in calcium fluxes. The model curves are reasonably close to experimental data; the parameters of the models are related to the properties of the entities responsible for control or maintenance of cytosolic calcium concentration. It has been shown that: (a) time-course of calcium concentration in cytosol of human platelets can be acceptably modeled on the basis of reasonable assumptions concerning agonist stimulated calcium redistribution in cellular compartments; (b) those assumptions are of fundamental importance for the model (c) some parameters of the model (taken arbitrarily) cannot be estimated independently of others from fitting the model to experimental data available; (d) special experiments are necessary to determine the unknown parameters; (e) agonist-stimulated change of the permeability of endomembrane of calcium stores can be regarded as a pulse of the permeability; it can be modeled as a sequence of transitions of the system from inactive to active and to inactive state again.

Diverse effects of ethanol on Ca2+ entry and subsequent aggregation of platelets

Although alcohol is known to inhibit platelet aggregation, and transplasmalemmal Ca(2+) entry is profoundly involved in platelet aggregation, there has been limited knowledge about the relationship between alcohol and Ca(2+) entry. The purpose of this study was to determine whether and how ethanol in vitro affects Ca(2+) entry through different pathways and the subsequent aggregation of platelets. Thapsigargin, 1-oleoyl-2-acetyl-sn-glycerol (OAG), and thrombin were used to stimulate human platelets. Ca(2)(+) entry and the subsequent aggregatory responses of platelets were measured by spectrofluorometry using fura-2/AM as an indicator and the light transmission method, respectively. Thapsigargin-induced Ca(2+) entry and the following platelet aggregation were significantly inhibited by ethanol at concentrations of 0.5% or more. OAG-induced Ca(2+) entry was significantly augmented by ethanol at concentrations of 0.5% or more, whereas platelet aggregation by OAG was significantly inhibited by ethanol at concentrations of 0.5 % or more. Thrombin-induced Ca(2+) entry was not significantly affected by ethanol up to 2%, whereas platelet aggregation by thrombin was markedly inhibited by ethanol at concentrations of 0.5% or more. Thrombin-induced Ca(2+) entry in the presence of SKF-96365 was augmented by pretreatment with ethanol. Ethanol in vitro showed diverse effects on the different Ca(2+) entry pathways of platelets, whereas aggregatory responses induced by activation of the different Ca(2+) entry pathways of platelets were all inhibited by ethanol. These results suggest that ethanol inhibits platelet aggregation mainly via a mechanism(s) other than transplasmalemmal Ca(2+) entry.

Sensitivity of thrombin-induced platelet aggregation to inhibition by ethanol

BACKGROUND

The purpose of this study was to determine the concentration of ethanol required for inhibition of thrombin-induced aggregation of human platelets in vitro.

METHODS

Three methods, light transmission method, particle counting method using light scattering and screen filtration pressure method using whole blood, were used for evaluation of platelet aggregation.

RESULTS

Thrombin (0.2 U/ml)-induced platelet aggregation was significantly inhibited by ethanol, and the threshold ethanol concentrations for inhibition determined by measurements using the light transmission method, particle counting method and screen filtration pressure method were 0.5%, 0.125% and 2%, respectively. Platelet aggregation induced by a lower concentration (0.05 U/ml) of thrombin was detected by the screen filtration pressure method but not by the light transmission method or particle counting method. The threshold ethanol concentration for the inhibition of thrombin (0.05 U/ml)-induced platelet aggregation was 0.125% according to results obtained by using the screen filtration pressure method.

CONCLUSIONS

Sensitivities for detection of thrombin-induced platelet aggregation and for detection of inhibition of platelet aggregation by ethanol were high in the screen filtration pressure method and the particle counting method, respectively. The threshold concentration of ethanol to inhibit thrombin-induced platelet aggregation is about 0.125% (approximately 21 mmol/l), which is easily attainable after drinking alcohol.

α-Bulnesene, a novel PAF receptor antagonist isolated from Pogostemon cablin

Alpha-bulnesene is a sesquiterpenoid isolated from the water extract of Pogostemon cablin. It showed a potent and concentration-dependent inhibitory effect on platelet-activating factor (PAF) and arachidonic acid (AA) induced rabbit platelet aggregation. In a radioligand binding assay for the PAF receptor, alpha-bulnesene competitively inhibited [(3)H]PAF binding to the PAF receptor with an IC(50) value of 17.62+/-5.68microM. alpha-Bulnesene also dose-dependently inhibited PAF-induced intracellular Ca(2+) increase in fluo-3/AM-loaded platelets (IC(50) values of 19.62+/-1.32microM). Furthermore, alpha-bulnesene inhibited AA-induced thromboxane B(2) (TXB(2)) formation and prostaglandin E(2) (PGE(2)) formation. These results indicate that the inhibitory effect of alpha-bulnesene on platelet aggregation was due to a dual activity; specifically the chemical blocked PAF-induced intracellular signal transduction and interfered with cyclooxygenase activity, which resulted in a decrease in thromboxane formation. This study is the first to demonstrate that alpha-bulnesene is a PAF receptor antagonist as well as an anti-platelet aggregation agent.

Intracellular Ca2+ homeostasis and aggregation in platelets are impaired by ethanol through the generation of H2O2 and oxidation of sulphydryl groups

The mechanisms involved in the effect of ethanol on Ca2+ entry and aggregability have been investigated in human platelets in order to shed new light on the pathogenesis of alcohol consumption. Ethanol (50 mM) induced H2O2 production in platelets by Ca2+-dependent and independent mechanisms. Ca2+ entry induced by ethanol was impaired by catalase. Ethanol reduced SOCE mediated by depletion of the 2,5-di-(tert-butyl)-1,4-hydroquinone (TBHQ)-sensitive acidic stores but enhances SOCE regulated by the dense tubular system. This effect was abolished by treatment with catalase or the sulphydryl group reducing agent dithiotreitol (DTT). Similarly, the anti-aggregant effect of ethanol was prevented by platelet treatment with catalase or DTT. In conclusion we provide considerable evidence that ethanol alters Ca2+ entry and reduces thrombin-induced aggregation as a result of the generation of H2O2 and the oxidation of sulphydryl groups in human platelets.