Cross-talking between lymphocytes and platelets and its regulation by nitric oxide and peroxynitrite in physiological condition and endotoxemia

Cross-talk between platelets and lymphocytes may play a role in different pathological conditions like sepsis. This study aimed to investigate the effect of lymphocytes on platelet aggregation in lipopolysaccharide (LPS)-stimulated and non-stimulated cells. Main methods: Lymphocytes and platelet-rich plasma (PRP) were obtained from rat arterial blood. Platelets (1.2 x 10(8) platelets/ml) were incubated with lymphocytes (0.8 x 10(6) cells/ml) in the presence or not of LPS (100 mu g/ml), after which ADP (5 mu M)-induced platelet aggregation was carried out. Key findings: Lymphocytes inhibited by 51% the platelet aggregation, which was significantly prevented by the non-selective NO inhibitor L-NAME (300 mu M) or the selective iNOS inhibitor 1400 W (100 mu M), as well as by the soluble guanylyl cyclase (sGC) inhibitor ODQ (10 mu M). The platelet inhibition by lymphocytes was accompanied by 2-fold increase of intraplatelet cGMP levels. Next, lymphocytes and platelets were co-incubated with LPS for 6 h. In LPS-treated cells, lymphocytes produced a larger inhibition of platelet aggregation (62%), despite the same elevation of cGMP levels (2.2-fold increase). This inhibitory effect was prevented by L-NAME and 1400 W, but rather unaffected by ODQ. The peroxynitrite (ONOO-) scavenger -(-)epigallocatechin gallate (ECG, 100 mu M) abolished the inhibition by lymphocytes on platelet aggregation in LPS-treated cells, but not in non-treated cells. Significance: Our results show that lymphocytes act to inhibit platelet aggregation via iNOS-derived NO release and cGMP generation. In presence of LPS, ONOO- production accounts for the platelet inhibition17227CNPQ – CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO470820/2008-