A structural basis for the inhibition of collagen‐stimulated platelet function by quercetin and structurally related flavonoids

• Published in: British journal of pharmacology 2010-03, Vol.159 (6), p.1312-1325
• Main Authors: Wright, Bernice, Moraes, Leonardo A, Kemp, Charles F, Mullen, William, Crozier, Alan, Lovegrove, Julie A, Gibbins, Jonathan M
• Format: Article
• Language: English
• Subjects: Biological and medical sciences; Blood Platelets - drug effects; Blotting, Western; Cardiovascular disease; Cells, Cultured; Collagen Type I - pharmacology; flavonoid inhibitory mechanisms; flavonoid metabolites; flavonoid structure; flavonoids; Flavonoids - chemistry; Flavonoids - pharmacology; Humans; Immunoprecipitation; Intracellular Signaling Peptides and Proteins - metabolism; Kinases; Medical sciences; Metabolites; Microscopy, Fluorescence; Pharmacology. Drug treatments; Phospholipase C gamma - metabolism; Phosphorylation; Platelet Aggregation - drug effects; Platelet Membrane Glycoproteins - metabolism; platelet signalling; Protein-Tyrosine Kinases - metabolism; Proto-Oncogene Proteins c-fyn - metabolism; Quercetin - chemistry; Quercetin - metabolism; Quercetin - pharmacology; Research Papers; Serotonin - metabolism; Signal Transduction - drug effects; Structure-Activity Relationship; Surface Plasmon Resonance; Syk Kinase
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.2009.00632.x

Background and purpose:  Molecular mechanisms underlying the links between dietary intake of flavonoids and reduced cardiovascular disease risk are only partially understood. Key events in the pathogenesis of cardiovascular disease, particularly thrombosis, are inhibited by these polyphenolic compounds via mechanisms such as inhibition of platelet activation and associated signal transduction, attenuation of generation of reactive oxygen species, enhancement of nitric oxide production and binding to thromboxane A2 receptors. In vivo, effects of flavonoids are mediated by their metabolites, but the effects and modes of action of these compounds are not well‐characterized. A good understanding of flavonoid structure–activity relationships with regard to platelet function is also lacking. Experimental approach:  Inhibitory potencies of structurally distinct flavonoids (quercetin, apigenin and catechin) and plasma metabolites (tamarixetin, quercetin‐3′‐sulphate and quercetin‐3‐glucuronide) for collagen‐stimulated platelet aggregation and 5‐hydroxytryptamine secretion were measured in human platelets. Tyrosine phosphorylation of total protein, Syk and PLCγ2 (immunoprecipitation and Western blot analyses), and Fyn kinase activity were also measured in platelets. Internalization of flavonoids and metabolites in a megakaryocytic cell line (MEG‐01 cells) was studied by fluorescence confocal microscopy. Key results:  The inhibitory mechanisms of these compounds included blocking Fyn kinase activity and the tyrosine phosphorylation of Syk and PLCγ2 following internalization. Principal functional groups attributed to potent inhibition were a planar, C‐4 carbonyl substituted and C‐3 hydroxylated C ring in addition to a B ring catechol moiety. Conclusions and implications:  The structure–activity relationship for flavonoids on platelet function presented here may be exploited to design selective inhibitors of cell signalling.