364 - Superior Targeted Anti-Platelet Activity of Nitrite

Abstract

Nitric Oxide (NO) is known to inhibit platelet activation and aggregation, primarily through activation of soluble guanylyl cyclase. Several NO donor drugs that take advantage of this pathway have been proposed to decrease platelet activation and thrombosis These include the S-nitrosothiols such as S-nitrosoglutathione (GSNO) and spontaneous NO releasing drugs such as diazeniumdiolates (also known as NONOates). More recently, the simple anion nitrite (NO2–) has been shown to inhibit platelet activation and aggregation in vitro and in vivo in rodents and humans. In this work, we compare the efficacy of one micromolar nitrite to that of one micromolar GSNO and one micromolar Diethylamine NONOate (DEANO) in inhibiting platelet activation and aggregation. Under normoxic conditions, nitrite had no effect on platelet activation while GSNO and DEANO significantly inhibited platelet activation. In the absence of red blood cells (that is in platelet rich plasma) nitrite again showed no activity whereas one micromolar GSNO and DEANO inhibited platelet activation. However, under hypoxic conditions, and in the presence of red blood cells, nitrite was as or more effective at inhibiting platelet activation than GSNO and DEANO. Nitrite was also as effective as GSNO and DEANO in inhibiting platelet aggregation in mixed venous blood. Whereas the presence of red blood cells is necessary for nitrite’s anti-platelet action, red blood cells reduced the efficacy of GSNO and DEANO. Importantly, physiological concentrations of NO and GSNO are three orders of magnitude below those used in these studies (one micromolar), but one micromolar nitrite is only 3-10 times resting physiological plasma levels and equal to that obtained after consumption of high nitrate containing foods or beverages. Thus, nitrite is an effective anti-platelet agent that is activated by red blood cells and has enhanced activities with physiological hypoxia. A nitrite-red blood cell-NO pathway may contribute to maintenance of normal hemostasis.