Effect of Aβ25～35 on ADP-induced platelet aggregation and intracellular calcium alteration

Objective To observe the effect of amyloid fragment 25～35 (Aβ25～35) on ADP induced platelet aggregation and intracytoplasmic calcium of platelet for studing the action of amyloid on plalelet. Methods The venous blood of 18 healthy volumteers was adopted and determined the maximal aggregating rate of platelet (PAGmax) induced by adding different concentration of ADP in various level of Aβ25～35 (0, 5, 10, 20, 40 μmol/L). The basal concentration of ADP for affecting platelet aggregation by amyloid was defined as 1 μmol/L (EC50, the concentration of ADP for 50% maximal platelet aggregation). The alteration of intracytoplasmic Ca2+ ([Ca2+]i) labelled by fluoresent calcium probe Fluo-3/AM was determined by different concentration of amyloid under confocal scanning microscope. Results 1) Adding ADP into platelet rich plasma, the maximum of EC50 (26.33±6.57)% was obtained when concentration of ADP was 1 μmol/L, thus it was defined as the basal ADP concentration in determing the Aβ25～35 for affecting platelet aggregation. 2) The ADP induced PAGmax increased in different extent before and after the action of Aβ25～35. The maximal platelet aggregation rate was gradually increased as the increasing concentration of Aβ25～35 (P 0.05). The highest platelet aggregation rate occurred in the group of 40 μmol/L Aβ25～35. The difference was significant (P 0.01) compared with adding ADP only (0 μmol/L Aβ25～35). 3) The platelet intracytoplasmic [Ca2+]i concentration increased after inducing by Aβ25～35 and its increasing level was according to the concentration of Aβ25～35. The most significant increasing level of platelet [Ca2+]i (P 0.01) established when existing 40 μmol/L Aβ25～35. Conclusion The effect of higher concentration of Aβ25～35 may promote ADP induced platelet aggregation and increases platelet ([Ca2+]i) concentraion. It shows that the promoting effect of Aβ25～35 on platelet aggregation might be associated with the increasing level of platelet intracytoplasmic Ca2+ level.