EFFECTS OF CYSTEINYL LEUKOTRIENES ON PLATELET ACTIVATION

Platelet are key players in haemostasis and represent a pivotal link between inflammation, immunity and atherogenesis. Cysteinyl leukotrienes (CysLTs) such as LTC4, LTD4, and LTE4 are potent lipid inflammatory mediators which interact with G protein-coupled receptors, CysLT1R, CysLT2R . However, LTE4, the most stable cystenyl leukotriene, is not putative substrate for these two receptor. Recently have been hypothesized that a third cystenyl leukotreine receptor exists, and a computer modeling suggests P2Y12, receptor for ADP present on platelet surface, as the putative receptor. But GPR99 is also hypothesized as LTE4 putative receptor. It is known that LTE4 needs P2Y12 on platelet to mediate inflammation in sensitized mice, and LTC4 can induce release of P-selectin in sensitized mice. In human platelet LTE4 cannot increase level of cAMP, or of p-selectin. Aim of this study was to test whether cystenyl leukotrienes elicit platelet functional responses, by interacting with the platelet P2Y12, receptor for ADP. We measure the platelet aggregation induced by CysLTs alone or in combination with epinephrine or ADP; the cAMP level in presence of PGE1, ADP and CysLTs, and finally the p-selectin expression on platelet surface after stimulation with ADP and CysLTs and in presence/absence of cangrelor. Ours results shows that CysLTs cannot affect platelet aggregation alone or in combination with other agonist, independently of presence of physiological level of calcium. CysLTs failed to show an effect also on cAMP level. Also when platelet activation was tested by measuring the expression of p-selectin on the platelet membrane induced by ADP, CysLTs failed to show any effect. The negative results of our studies are not due to alterations of the CysLTs that we used, as they were identified correctly at mass spectrometry and induced normal cellular response of HUVEC, as previously shown. The inflammatory effects of CysLTs mediated by the platelet P2Y12 receptor, which have been demonstrated in vivo experiments, were most likely indirect, rather than induced by a direct interaction of CysLTs with platelets.