Inhibition of PAR4 signaling mediates ethanol-induced attenuation of platelet function in vitro.
BACKGROUND
Reduction in coronary heart disease morbidity in response to moderate consumption of alcoholic beverages may be partly mediated by ethanol-induced inhibition of platelet function. However, the precise mechanisms by which ethanol modulates platelet activation induced by thrombin, which plays a central role in hemostasis, remain unclear. The goal of this study was to investigate ethanol-induced changes in platelet function and clarify the underlying mechanisms including PAR1 and PAR4 activity and [Ca2+]i dynamics in vitro.


METHODS
Platelet aggregation, increase in intracellular calcium ([Ca2+]i), and release of platelet factor 4 and beta-thromboglobulin induced by alpha-thrombin, PAR1-agonist peptide (AP), or PAR4-AP were assessed in the presence or absence of ethanol.


RESULTS
Ethanol exposure inhibited low-dose thrombin (0.5 nM)-induced aggregation but not an increase in [Ca2+]i. In contrast, ethanol had no effect on high-dose thrombin (10 nM)-induced aggregation or the [Ca2+]i increase. Ethanol did not significantly inhibit thrombin-induced release of platelet factor 4 and beta-thromboglobulin. Ethanol reduced PAR1-AP-induced aggregation, but did not affect the spike form of [Ca2+]i increase. In contrast, ethanol inhibited the increase in [Ca2+]i as well as the aggregation in response to PAR4-AP and resulted in delayed [Ca2+]i peak time. Furthermore, ethanol inhibited both PAR1-AP- and PAR4-AP-induced platelet factor 4 and beta-thromboglobulin release.


CONCLUSIONS
These data suggest that ethanol inhibits platelet aggregation via inhibition of PAR4 signaling and subsequent inhibition of Ca2+ influx and granule release. This phenomenon may contribute to the reduction in coronary heart disease morbidity in response to consumption of alcoholic beverages.
Kasuda
Shogo
S
Department of Legal Medicine, Nara Medical University School of Medicine, Kashihara, Nara, Japan.
Sakurai
Yoshihiko
Y
Shima
Midori
M
Morimura
Yoshifumi
Y
Kudo
Risa
R
Takeda
Tomohiro
T
Ishitani
Akiko
A
Yoshioka
Akira
A
Hatake
Katsuhiko
K
D001792:Blood Platelets / Q000187:drug effects*; D002118:Calcium / Q000378:metabolism; D002492:Central Nervous System Depressants / Q000494:pharmacology*; D000431:Ethanol / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D010974:Platelet Aggregation / Q000187:drug effects; D010978:Platelet Factor 4 / Q000378:metabolism; D018179:Receptors, Thrombin / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects*; D013917:Thrombin / Q000502:physiology; D001620:beta-Thromboglobulin / Q000378:metabolism; D010975:Platelet Aggregation Inhibitors
D002492:Central Nervous System Depressants; D018179:Receptors, Thrombin; D001620:beta-Thromboglobulin; D010978:Platelet Factor 4; D000431:Ethanol; D013917:Thrombin; C112908:protease-activated receptor 4; D002118:Calcium; D010975:Platelet Aggregation Inhibitors