Myricetin, the Main Flavonoid in Syzygium cumini Leaf, Is a Novel Inhibitor of Platelet Thiol Isomerases PDI and ERp5.

Renato Simões Gaspar,Shuruq Alsufyani,João Lucas De Lima Fontelles,Samira Abdalla Da Silva,Andrés Trostchansky,Hiran Reis Sousa,Vinicyus Teles Chagas,Jennifer Stapleton,Antonio Marcus De Andrade Paes,Jonathan M Gibbins

doi:10.3389/fphar.2019.01678

Abstract

BackgroundFlavonoids have been characterized as a prominent class of compounds to treat thrombotic diseases through the inhibition of thiol isomerases. Syzygium cumini is a flavonoid-rich medicinal plant that contains myricetin and gallic acid. Little is known about the potential antiplatelet properties of S. cumini and its constituent flavonoids.ObjectiveTo evaluate the antiplatelet effects and mechanism of action of a polyphenol-rich extract (PESc) from S. cumini leaf and its most prevalent polyphenols, myricetin and gallic acid.MethodsPESc, myricetin, and gallic acid were incubated with platelet-rich plasma and washed platelets to assess platelet aggregation and activation. In vitro platelet adhesion and thrombus formation as well as in vivo bleeding time were performed. Finally, myricetin was incubated with recombinant thiol isomerases to assess its potential to bind and inhibit these, while molecular docking studies predicted possible binding sites.ResultsPESc decreased platelet activation and aggregation induced by different agonists. Myricetin exerted potent antiplatelet effects, whereas gallic acid did not. Myricetin reduced the ability of platelets to spread on collagen, form thrombi in vitro without affecting hemostasis in vivo. Fluorescence quenching studies suggested myricetin binds to different thiol isomerases with similar affinity, despite inhibiting only protein disulfide isomerase (PDI) and ERp5 reductase activities. Finally, molecular docking studies suggested myricetin formed non-covalent bonds with PDI and ERp5.ConclusionsPESc and its most abundant flavonoid myricetin strongly inhibit platelet function. Additionally, myricetin is a novel inhibitor of ERp5 and PDI, unveiling a new therapeutic perspective for the treatment of thrombotic disorders.

Highlights

Cardiovascular diseases are the leading cause of death worldwide, a scenario where thrombosis and its associated outcomes account for one in four deaths (Wendelboe and Raskob, 2016)
Different concentrations of polyphenol-rich extract from S. cumini (PESc) were incubated with platelet-rich plasma (PRP) and platelets were activated with various agonists
Increased agonist concentration partially overcame the inhibition seen in adenosine diphosphate (ADP)- and thrombin-induced platelet aggregation (Supplementary Figure 2)

Summary

Introduction

Cardiovascular diseases are the leading cause of death worldwide, a scenario where thrombosis and its associated outcomes account for one in four deaths (Wendelboe and Raskob, 2016). Platelets play a key role in arterial thrombosis, due to platelet aggregation triggered by multiple agonists, such as adenosine diphosphate (ADP), thrombin, and collagen These signaling pathways will inevitably culminate in the activation of the platelet surface integrin aIIbb (Banno and Ginsberg, 2008; Ghoshal and Bhattacharyya, 2014), which becomes activated after the isomerization of critical disulfide bonds on its extracellular b domain. This process is thought to be mediated by protein disulfide isomerase (PDIA1, referred to as PDI) and sibling proteins (Essex, 2008). Little is known about the potential antiplatelet properties of S. cumini and its constituent flavonoids

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