Polyphenol Rich Extract of Syzygium cumini (L.) Skeels Leaves Decreases Platelet Aggregation and Inhibits Reductase Activity of Protein Disulfide Isomerase.

Abstract

Platelet agreggation results from conformational changes in αIIbβIII integrin, which are dependent on protein disulfide isomerase (PDI) activity. Recently, PDI inhibition has been proposed as an antithrombotic mechanism, for that polyphenolic compounds have emerged as potential inhibitors. Our group has demonstrated that Syzygium cumini (L.) Skeels (Myrtacea) leaf contains multiple polyphenols, such as: gallic acid, miricetyn‐3‐a‐arabinoside, mirycetin deoxiexoside and quercetin‐3‐glycoside; which enable this species for anti‐platelet activity. Therefore, this study aimed to evaluate the effects of polyphenol rich extract (ERP) from S. cumini leaf on platelet aggregation and PDI reductase activity. Platelet‐rich plasma (PRP) from healthy volunteers (n=5) was incubated with ERP for 25 min at concentrations ranging from 10 to 1000μg/mL, previously to activation with 2.5 or 5μM ADP. ERP at the higher concentration inhibited platelet aggregation in 66 and 33%, respectively. Under thrombin stimulus (0.01 and 0.02 U/mL), ERP (1000 μg/mL) reduced platelet aggregation in ca. 35%. Moreover, ERP also inhibited PMA‐induced platelet aggregation by 29% in its higher concentration. To analyze the ERP effect on αIIbβIII integrin activation, flow citometry protocols were conducted in washed platelets similarly pre‐treated with ERP (10, 100 and 1000μg/mL) before activation with thrombin (0.02U/mL) and tagged with PAC–1 FITC antibody. ERP dose‐dependently reduced the integrin activation in presence of 10 μg/mL (21%), 100 μg/mL (27%) and 1000 μg/mL (33%). Finally, ERP effects on PDI reductase activity were also assessed at concentrations ranging from 0.1 to 100 μg/mL. A maximum inhibitory effect on PDI reductase activity of 77% was found for the higher concentration. Therefore, our data supports that ERP‐containing polyphenols from S. cumini leaf reduce platelet aggregation, probably through PDI inhibition, which demonstrates its prominent anti‐platelet property.Support or Funding InformationFinancial support: FAPEMA; UFMA