Figure 4.

Flavonoids and metabolites block total protein tyrosine phosphorylation in intact platelets: the C ring C-3 hydroxyl group is necessary for potent inhibition. Washed human platelets (8 × 10⁸ cells·mL⁻¹) treated with 1 mM EGTA were pretreated with increasing concentrations of flavonoids (quercetin: A, B and apigenin: D), metabolites [tamarixetin: B, quercetin-3′-sulphate (Q-3′-S): C and quercetin-3-glucuronide (Q-3-G): C] or solvent control [DMSO (0.2% v/v)] for 5 min. Platelets were stimulated with 25 µg·mL⁻¹ collagen for 90 s before the immunodetection of total protein tyrosine phosphorylation, as a percentage of the DMSO-treated, collagen-stimulated control (100%). The bars represent the mean (n= 3) tyrosine phosphorylation for each treatment (±SEM). *P≤ 0.05, **P≤ 0.01 and ***P≤ 0.001 compared with the control (DMSO-treated, collagen-stimulated platelets).