Inhibitory Effects of Rice Bran Water Extract Fermented Lactobacillus plantarum due to cAMP-dependent Phosphorylation of VASP (Ser157) on human Platelet Aggregation

In this study, we investigated the effect of rice bran water extract fermented with Lactobacillus plantarum KCCM-12116 (RBLp) on ADP ($20{\mu}M$)-, collagen ($10{\mu}g/mL$)-, and thrombin (0.2 U/mL)-stimulated platelet aggregation. RBLp dose-dependently inhibited ADP-, collagen-, and thrombin-induced platelet aggregation, with $IC_{50}$ values of 501.1, 637.2, and > $2,000{\mu}g/mL$, respectively. The platelet aggregation induced by ADP plus RBLp ($750{\mu}g/mL$) was increased by the adenylate cyclase inhibitor, SQ22536, and the cAMP-dependent protein kinase (A-kinase) inhibitor, Rp-8-Br-cAMPS. Treatment with RBLp increased the phosphorylation of VASP ($Ser^{157}$), an A-kinase substrate, which was also inhibited by SQ22536 and Rp-8-Br-cAMPS. It is thought that the RBLp-induced increases in cAMP contributed to the phosphorylation of VASP ($Ser^{157}$), which in turn resulted in an inhibition of ADP-induced platelet aggregation, thereby indicating that RBLp has an antiplatelet effect via cAMP-dependent phosphorylation of VASP ($Ser^{157}$). Thus, RBLp may have therapeutic potential for the treatment (or prevention) of platelet aggregation-mediated diseases, such as thrombosis, myocardial infarction, atherosclerosis, and ischemic cerebrovascular disease.