Specific inhibition of PAF-acether-induced platelet activation by BN 52021 and comparison with the PAF-acether inhibitors kadsurenone and CV 3988

BN 52021 is a chemically defined substance extracted from Ginkgo biloba leaves. Its inhibitory potency was tested on washed human platelets prepared so as to render them specifically sensitivity either to adenosine 5′-diphosphate (ADP), arachidonic acid (AA) or PAF-acether. Its activity and specificity were compared with those of two other reported inhibitors of PAF-acether effects: Kadsurenone and CV 3988. PAF-acether-induced aggregation of washed human platelets was concentration dependently inhibited by BN 52021 (IC 50: 2.22 ± 0.79 μM against 7.5 nM PAF-acether (n = 3)). Under the same experimental conditions the aggregation triggered by ADP was not modified and that induced by AA was marginally affected. The PAF-acether EC 50 in platelet-rich plasma was increased 5- and 46-fold with 1 μM and 5 μM of BN 52021 respectively. This strongly suggested that the mechanism of action of BN 52021 is of the competitive type. Analysis of [ 3H]PAF-acether binding showed that BN 52021 as well as unlabelled PAF-acether prevented [ 3H]PAF-acether binding to intact washed platelets. In washed human platelets Kadsurenone affected only PAF-acether-induced aggregation (IC 50: 0.8 ± 0.4 μM (n = 3)), whereas CV 3988 inhibited the aggregation induced by ADP, AA and PAF-acether (IC 50 were 10.2 ± 2.3 μM; 2.2 ± 0.1 μM; 1.0 ± 0.1 μM respectively (n = 3). In contrast, up to 30 μM, CV 3988 was a specific antagonist of PAF-acether-induced platelet aggregation in plasma. IC 50 in plasma were 3.3 ± 1.8, 19.6 ± 10.4 and 27.6 ± 9.3 μM (n = 3) for BN 52021, Kadsurenone and CV 3988 respectively. Thus, both in plasma and aqueous medium, BN 52021 and Kadsurenone are specific inhibitors of PAF-acether effectts on platelets, whereas CV 3988 is a specific anti-PAF-acether only in PRP. Of the three compounds, BN 52021 is the most potent inhibitor of PAF-acether-induced aggregation in platelet-rich plasma.