Abstract

Twenty-two methanol extracts from different parts of nine Garcinia species were investigated for their ability to inhibit platelet aggregation and low-density lipoprotein (LDL) peroxidation and their total phenolic contents (TPC). The antioxidant activity of the extracts was examined using thiobarbituric acid reactive substances (TBARS) assay with human LDL as the oxidation substrate and their antiplatelet activity in human whole blood was determined by using an electrical impedance method. The TPC of the extracts were measured by the Folin-Ciocalteau method. Among all samples studied, the leaf extract ofGarcinia eugenifolia Wall showed the highest inhibitory activity on LDL peroxidation with IC₅₀ value of 12.5 µg/ml. The twig extract of Garcinia mangostana Linn. was the most effective sample against platelet aggregation caused by arachidonic acid (AA) with IC₅₀value of 15.6 µg/ml. The TPC of the extracts varied from 4.4 to 62.8 mg of gallic acid equivalents per g (mg GAE/g). The Pearson correlation analysis revealed that TPC showed moderate positive correlations with antioxidant (r = 0.30, p < 0.05) and antiplatelet activities (AA-induced, r = 0.62, p < 0.05; ADP-induced, r = 0.42, p < 0.05; collagen-induced, r = 0.54, p < 0.05). Thus, it was concluded that the antioxidant and antiplatelet activities of theGarcinia extracts could partly be due to their total phenolic contents.

Key words: Garcinia species, low-density lipoprotein, LDL antioxidant activity, antiplatelet activity, total phenolic contents.