Complex effects of different green tea catechins on human platelets.
Epigallocatechin gallate (EGCG), a major component of green tea, has been previously shown to inhibit platelet aggregation. The effects of other green tea catechins on platelet function are not known. Pre-incubation with EGCG concentration-dependently inhibited thrombin-induced aggregation and phosphorylation of p38 mitogen-activated protein kinase and extracellular signal-regulated kinases-1/2. In contrast EGCG stimulated tyrosine phosphorylation of platelet proteins, including Syk and SLP-76 but inhibited phosphorylation of focal adhesion kinase. Other catechins did not inhibit platelet aggregation. Interestingly, when EGCG was added to stirred platelets, a tyrosine kinase-dependent stimulation of platelet aggregation was observed. The two other catechins containing a galloyl group in the 3' position (catechin gallate, epicatechin gallate) also stimulated platelet aggregation, while catechins without a galloyl group (catechin, epicatechin) or the catechin with a galloyl group in the 2' position (epigallocatechin) did not.
Lill
Gereon
G
Institut für Pharmakologie und Klinische Pharmakologie, Universitätsklinikum Düsseldorf, Moorenstr 5, D-40225 Düsseldorf, Germany.
Voit
Simone
S
Schrör
Karsten
K
Weber
Artur-Aron
AA
D001792:Blood Platelets / Q000187:drug effects*; D002392:Catechin / Q000031:analogs & derivatives* / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D010766:Phosphorylation; D010974:Platelet Aggregation / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013662:Tea / Q000737:chemistry*; D013917:Thrombin / Q000494:pharmacology; D014443:Tyrosine / Q000378:metabolism
D013662:Tea; D014443:Tyrosine; D002392:Catechin; C045651:epigallocatechin gallate; D013917:Thrombin