Gallic acid antagonizes P-selectin-mediated platelet-leukocyte interactions - Implications for the French paradox

Background - Current paradigm attributes the low incidence of cardiovascular disorders in Mediterranean countries despite a high saturated fat intake, the "French paradox," to the antioxidant capacity of red wine polyphenols. Conceivably, other antiinflammatory pathways may contribute to at least a similar extent to the atheroprotective activity of these polyphenols. We have investigated whether gallic acid (GA), an abundant red wine polyphenol, modulates the activity of P-selectin, an adhesion molecule that is critically involved in the recruitment of inflammatory cells to the vessel wall and thus in atherosclerosis. Methods and Results - GA potently inhibited the binding of a peptide antagonist (IC50, 7.2 mumol/L) and biotin-PAA-Le(a)SO(3)H, an established high-affinity ligand, to P-selectin (IC50, 85 mumol/L). Under dynamic flow conditions, GA markedly and dose dependently attenuated the rolling of monocytic HL60 cells over P-selectin-transfected Chinese hamster ovary cells (EC50, 14.5 mumol/L) while increasing the velocity of P-selectin-dependent rolling of human blood leukocytes over a platelet monolayer. In vivo tests established that GA administration to normolipidemic C57/B16 and aged atherosclerotic apolipoprotein E - deficient mice impaired the baseline rolling of conjugates between activated platelets and circulating monocytes over femoral vein endothelium, as judged by online video microscopy (ED50, 1.7+/-0.3 and 1.5+/-0.4 mg . kg(-1) . h(-1), respectively). Conclusions - Our findings provide a solid mechanistic foundation through which GA intervenes in major inflammatory pathobiologies by binding and antagonizing P-selectin.