Allicin and disulfiram enhance platelet integrin αIIbβ3-fibrinogen binding

Introduction: Activation of the platelet receptor αIIbβ3 (glycoprotein IIbIIIa) involves a change in the disulfide bonds pattern in the extra-cellular domain of the receptor. The disulfide-bond reducing agent, dithiothreitol (DTT), can increase integrin activity, and point mutations of specific cysteine residues of the integrin can cause its lockage at the high affinity state. The present study is aimed to support the hypothesis that prevention of specific αIIbβ3 intra-molecular disulfide bond formation increases receptor-ligand binding activity. Methods: Platelet aggregation was induced by collagen or ADP and epinephrine. Integrin αIIbβ3-fibrinogen binding was evaluated on prostaglandins E₁ (PGE₁)-treated washed platelets or baby hamster kidney (BHK) cells expressing human αIIbβ3. Integrin was directly activated by an anti-ligand induced binding site (LIBS) PT25-2 antibody. The effect of sulfhydryl-reactive agents, such as allicin, glutathione, dithiobis nitrobenzoic acid (DTNB) and disulfiram, was tested on αIIbβ3 activity. Results: Allicin (40 μM) completely inhibited washed platelets agonist-induced aggregation. Both allicin and disulfiram (40 μM) inhibited αIIbβ3-fibrinogen binding and P-selectin expression in washed platelets. However, there was an increase in αIIbβ3-fibrinogen binding but not P-selectin expression in PGE₁-treated washed platelets activated by PT25-2 antibody. At a high concentration (400 μM) both inhibited αIIbβ3-fibrinogen binding. Similarly, in BHK cells expressing αIIbβ3 activated by PT25-2 antibody, allicin at a low concentration increased αIIbβ3 activity. Conclusions: Allicin and disulfiram inhibit agonist-induced washed platelet activation probably via inhibition of platelet signaling, but enhance PT25-2 antibody-induced αIIbβ3 integrin activity most likely by preventing reformation of disulfide bridges thereby stabilizing the active conformation of the integrin.