Abstract 11864: Inorganic Nitrate Attenuates Platelet Reactivity in Healthy Males but not Females: Role of the Erythrocyte and Cyclic GMP
Background: Aspirin is no longer recommended in primary prevention of atherothrombosis in non-diabetics due to bleeding risk. Studies suggest that dietary nitrate, via its reduction in vivo to nitrite and then nitric oxide (NO), may provide a safe, natural but moderate alternative. Objective: To determine whether low dose inorganic nitrate supplementation attenuates platelet reactivity and to elucidate the mechanisms involved.
Methods: We conducted a randomised double-blind crossover study in 24 (12 of each sex) healthy subjects of potassium nitrate (KNO3, 8mmol) vs potassium chloride (KCL, 8mmol placebo) capsules. Samples were collected before and 3h after ingestion. Whole blood impedence aggregometry and platelet p-selectin expression using flow cytometry in response to saline control, ADP (10µM) and collagen (3µg/ml) were measured. [Nitrite] and [nitrate] were measured using ozone chemiluminescence. To identify the site of nitrite reduction within the blood, whole blood or platelet-rich plasma (PRP) of a further 12 males and 6 females were incubated with nitrite (as KNO2) and effects determined. Platelet pellets were generated and cGMP levels determined using ELISA.
Results: Sex did not alter ADP (56.4±2.5Ωs) or collagen (72.0±3.0Ωs) induced platelet aggregation whilst p-selectin expression in response to ADP was substantially lower in females (p<0.01). Following KNO3, plasma, salivary and urinary [nitrite] and [nitrate] were significantly elevated above baseline in males and females, with no changes following KCL. ADP-induced aggregation was reduced (∼24% P<0.01) after KNO3 in males only, an effect associated with ∼2-fold (p<0.01) rise in platelet cGMP in males. KNO2 treatment ex-vivo caused concentration-dependent reduction of ADP-induced aggregation (max effect ∼32% inhibition, P<0.05, n=12) in male blood only and platelet cGMP was likewise elevated (p<0.05). In contrast incubation of PRP with KNO2 had no effect on platelet aggregation.
Conclusion: KNO3 supplementation attenuates platelet reactivity of healthy males but not females due to erythrocytic nitrite-derived NO-induced elevations of platelet cGMP. Nitrate supplementation may provide an alternative option in anti-platelet medication in primary prevention.
- © 2012 by American Heart Association, Inc.