Antiplatelet effect of spironolactone via modulation of cPLA 2 -mediated thromboxane A 2 generation in murine platelets

Importance: Spironolactone, a steroidal aldosterone antagonist, is widely used as a diuretic and antihypertensive agent.Steroids have been known to promote thrombosis by directly increasing platelet count and activation and indirectly by increasing oxidative stress and suppressing nitric oxide synthesis.However, the effects of spironolactone on platelet activation remain unclear.Objective: To investigate the effects of spironolactone on platelet function and underlying signaling mechanisms.Methods: Platelet aggregation, dense granule secretion, thromboxane A 2 (TxA 2 ) generation, and protein phosphorylation were evaluated in platelets treated with spironolactone.Results: Spironolactone significantly inhibited the secondary wave of platelet aggregation and dense granule secretion induced by 2-methylthioadenosine diphosphate (2-MeSADP).It is known that 2-MeSADP-induced secretion and the resultant secondary wave of aggregation depend on TxA 2 -mediated positive feedback, suggesting a role for spironolactone in regulating TxA 2 generation in platelets.Additionally, spironolactone did not affect 2-MeSADP-induced platelet aggregation in aspirin-treated platelets in which TxA 2 generation was blocked.Furthermore, platelet aggregation and secretion induced by low concentrations of thrombin, which are also affected by TxA 2 -mediated positive feedback, were partially inhibited by spironolactone.Notably, spironolactone significantly suppressed TxA 2 generation induced by both 2-MeSADP and thrombin.Finally, spironolactone markedly inhibited the 2-MeSADPand thrombin-induced phosphorylation of cytosolic phospholipase A 2 (cPLA 2 ), extracellular signal-regulated kinase, and protein kinase B in non-aspirin-treated platelets, whereas only cPLA 2 phosphorylation was significantly inhibited in aspirin-treated platelets.Conclusions and Relevance: Spironolactone inhibits platelet activation by suppressing TxA 2 generation, primarily by modulating cPLA 2 phosphorylation, providing mechanistic insight into its effects on platelet signaling in vitro.