Abstract

This study was designed to investigate the activity of ethyl acetate extract from Opuntia humifusa Raf. (OH-EAE) in ligand-activated platelet aggregation. Platelet aggregation was induced either by ADP, a potent agonist to platelet G protein-coupled P2Y receptor, by collagen, a potent ligand that activates platelet integrin α2β1 and glycoprotein VI, or thrombin, a platelet protease-activated receptors subtype I and IV. The OH-EAE inhibited platelet aggregation induced by ADP (10 μM) in a dose dependent manner. In addition, OH-EAE significantly and dose-dependently inhibited collagen (2.5 μg/ml)- and thrombin (0.05 U/ml)-induced platelet aggregation. Moreover, the downstream signaling analysis revealed that the extract potently inhibited ADP-induced intracellular calcium mobilization ([Ca²⁺l_i). Since degranulation is a marker of platelet activation, the extract effect on the dense granule secretary activity was evaluated. As such, OH-EAE strongly suppressed ADP-induced ATP release. This preliminary result suggests that O. humifusa may be taken as a candidate lead natural compound to be considered in the search for natural products with beneficial effects on aberrant platelet activation mediated cardiovascular disorders.

Key words: Opuntia humifusa extract, calcium, rat platelets, platelet agonists.

Abbreviation

OH-EAE, Ethyl acetate extract from Opuntia humifusa Raf.; GP VI,glycoprotein VI; PLCβ, Phospholipase Cβ; DAG, diacylglycerol; PKC, protein kinase C;PAR, Protease-activated receptor; ATP, Adenosine triphosphate.