In vitro inhibition of human and rat platelets by NO donors, nitrosoglutathione, sodium nitroprusside and SIN-1, through activation of cGMP-independent pathways

Abstract

Three different NO donors, S-nitrosoglutathione (GSNO), sodium nitroprusside (SNP) and 3-morpholino-sydnonimine hydrochloride (SIN-1) were used in order to investigate mechanisms of platelet inhibition through cGMP-dependent and -independent pathways both in human and rat. To this purpose, we also evaluated to what extent cGMP-independent pathways were related with the entity of NO release from each drug.SNP, GSNO and SIN-1 (100μM) effects on platelet aggregation, in the presence or absence of a soluble guanylate cyclase inhibitor (ODQ), on fibrinogen receptor (αIIbβ3) binding to specific antibody (PAC-1), and on the entity of NO release from NO donors in human and rat platelet rich plasma (PRP) were measured.Inhibition of platelet aggregation (induced by ADP) resulted to be greater in human than in rat. GSNO was the most powerful inhibitor (IC50 values, μM): (a) in human, GSNO=0.52±0.09, SNP=2.83±0.53, SIN-1=2.98±1.06; (b) in rat, GSNO=28.4±6.9, SNP=265±73, SIN-1=108±85. GSNO action in both species was mediated by cGMP-independent mechanisms and characterized by the highest NO release in PRP. SIN-1 and SNP displayed mixed mechanisms of inhibition of platelet aggregation (cGMP-dependent and independent), except for SIN-1 in rat (cGMP-dependent), and respectively lower or nearly absent NO delivery. Conversely, all NO-donors prevalently inhibited PAC-1 binding to αIIbβ3 through cGMP-dependent pathways.A modest relationship between NO release from NO donors and cGMP-independent responses was found. Interestingly, the species difference in NO release from GSNO and inhibition by cGMP-independent mechanism was respectively attributed to S-nitrosylation of non-essential and essential protein SH groups.