Inhibitory Effects of Epigallocatechin-3-Gallate on Microsomal Cyclooxygenase-1 Activity in Platelets

Abstract

In this study, we investigated the effect of (–)-epigallocatechin-3-gallate (EGCG), a major component of green tea catechins from green tea leaves, on activities of cyclooxygenase (COX)-1 and thromboxane synthase (TXAS), thromboxane A2 (TXA2) production associated microsomal enzymes. EGCG inhibited COX-1 activity to 96.9%, and TXAS activity to 20% in platelet microsomal fraction having cytochrome c reductase (an endoplasmic reticulum marker enzyme) activity and expressing COX-1 (70 kDa) and TXAS (58 kDa) proteins. The inhibitory ratio of COX-1 to TXAS by EGCG was 4.8. These results mean that EGCG has a stronger selectivity in COX-1 inhibition than TXAS inhibition. In special, a nonsteroid anti-inflammatory drug aspirin, a COX-1 inhibitor, inhibited COX-1 activity by 11.3% at the same concentration (50 μM) as EGCG that inhibited COX-1 activity to 96.9% as compared with that of control. This suggests that EGCG has a stronger effect than that of aspirin on inhibition of COX-1 activity. Accordingly, we demonstrate that EGCG might be used as a crucial tool for a strong negative regulator of COX-1/TXA2 signaling pathway to inhibit thrombotic disease-associated platelet aggregation.

Antioxidants from black and green tea: from dietary modulation of oxidative stress to pharmacological mechanisms

“…Regarding the reported inhibition of COX‐1 activity in platelets (Lee et al , ; Table ), this effect is not supported by the results of a human study conducted by Hirano‐Ohmori et al (). After the consumption of seven cups of GT a day for 2 weeks by healthy subjects, no significant changes in the aggregation of platelets were observed, despite a significant decrease in the serum low density lipoproteins (MDA‐LDL).…”

An Update on the Health Benefits of Green Tea

“…Many of the studies on platelet aggregation have been carried out using various animal platelets. In addition to showing that green tea catechins were involved in inhibition of platelet aggregation, studies suggested that catechins may affect several cellular targets that are related to platelet activation, including: through the arachadonic acid pathway, inhibition of a cytoplasmic increase in calcium, decreased thrombaxane A 2 (TXA 2 ) production, and inhibition of cyclooxygenase-1 (COX)-1 [90][91][92][93]. A study using human platelets concluded that EGCG was able to inhibit platelet activation by adenosine diphosphate (ADP) stimulation, and suppressed the p38 MAPK phosphorylation of heat shock protein 27 (HSP27), which would inhibit the release of pro-thrombotic contents from platelets [94].…”

Antiplatelet Effects of Caffeic Acid Due to Ca2＋ MobilizationInhibition Via cAMP-Dependent Inositol-1, 4, 5-Trisphosphate Receptor Phosphorylation

“…In a previous study, we reported that chlorogenic acid (50 μM), an analogue of CAFA, inhibits the COX-1 activity in platelets to 69.7% compared with that observed (52.5±2.5 pmoL/ min/protein-mg) in the controls in vitro 36) . In addition, the COX-1 inhibitor aspirin (50 μM) inhibited the COX-1 activity in platelets to 11.3% compared with that observed (1.59 nmoL/min/protein-mg) in the controls in vitro 12) . An autacoidal molecule, TXA2, produces IP3 to mobilize [Ca 2＋ ]i via the G-protein coupled receptor/PLC-β pathway to constrict the vessel tract 7,8,35,[37][38][39] , which enforces thrombus formation.…”

“…A polyphenolic compound, (-)-epigallocatechin-3-gallate (EGCG), in green tea is known to produce cAMP via adenylate cyclase activation and subsequently phosphorylate vasodilator-stimulated phosphoprotein (VASP)-Ser 157 via A-kinase activation to inhibit [Ca 2＋ ]i mobilization and TXA2 production on collageninduced platelet aggregation 11) . The inhibition of TXA2 production by EGCG is involved in the inhibition of COX-1 12) . With regard to the effects of a phenolic compound, caffeic acid (CAFA, Fig.…”