In Vitro Inhibitory Effect of Rubraxanthone Isolated from Garcinia parvifolia on Platelet-Activating Factor Receptor Binding

Abstract

Rubraxanthone and isocowanol isolated from Garcinia parvifolia Miq. were investigated for their inhibitory effects on platelet-activating factor (PAF) binding to rabbit platelets using ³ H-PAF as a ligand. Rubraxanthone showed a strong inhibition with IC₅₀ value of 18.2 μM. The IC₅₀ values of macluraxanthone, 6-deoxyjacareubin, 2-(3-methylbut-2-enyl)-1,3,5-trihydroxyxanthone, 2-(3-methylbut-2-enyl)-1,3,5,6-tetrahydroxyxanthone and 1,3,5-trihydroxy-6,6′-dimethylpyrano(2′,3′:6,7)-4-(1,1-dimethylprop-2-enyl)-xanthone were also determined for comparison. In the course of our study on structure-activity relationship of xanthones, the results revealed that a geranyl group substituted at C-8 was beneficial to the binding while a hydroxylated prenyl group at C-4 resulted in a significant loss in binding to the PAF receptor.

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