Potent platelet aggregation inhibitor from Trimeresurus gramineus snake venom

Using DEAE-Sephadex A-50 column chromatography and gel filtration, a potent platelet aggregation inhibitor from Trimeresurus gramineus venom was purified. It was an acidic phospholipase a, rich in aspartic acid, glutamic acid and half-cystine, with an isoelectric point of 3.6. At a concentration of 10 μg/ml, the purified inhibitor showed a marked inhibitory effect on platelet aggregations induced by adenosine diphosphate, collagen, sodium arachidonate and ionophore A-23187 in rabbit platelet-rich plasma, washed platelet suspension, as well as in thrombin-degranulated platelet suspension. The ID₅₀ of this venom inhibitor was about 2.5–5 μg/ml in platelet aggregations induced by all these aggregation inducers. The action of this inhibitor could be partially antagonized by phosphatidylethanolamine. High concentration of Ca²⁺ (5 mM) did not reverse the inhibitory action even in the presence of ionophore A-238187. The ¹⁴C]serotonin release induced by sodium arachidonate and thrombin was unaffected. Malonic dialdehyde formation induced by these aggregation inducers remained unchanged. Basal and prostaglandin E₁-stimulated cAMP levels were not altered by this inhibitor. No lactate dehydrogenase was released even at a concentration of 62.5 μg/ml. Polylysine-induced platelet agglutination was not affected. β-Mercaptoethanol inactivated both its phospholiase A enzymatic and platelet inhibitory activities, while p-bromophenacyl bromide only inactivated the former activity. The possibility of acting on a common final step of platelet aggregation, i.e. the intercellular adhesion between the activated platelets, was proposed.