Copyright © 2007, European Society of Cardiology
Age decreases nitric oxide synthesis and responsiveness in human platelets and increases formation of monocyte–platelet aggregates
Department of Clinical Pharmacology, Cardiovascular Division, School of Medicine, King's College London, London, UK
* Corresponding author. 3.07 Franklin–Wilkins Building, King's College London, 150 Stamford Street, London SE1 9NH, UK. Tel.: +44 20 7848 4283; fax: +44 20 7848 6220. albert.ferro{at}kcl.ac.uk
Objective Ageing is associated with an increase in atherothrombotic disease. Platelet-derived nitric oxide (NO) inhibits platelet activation, but the effect of age on platelet NO signaling is unknown. We investigated platelet NO biosynthesis and responsiveness in older (>45 years old) as compared with younger (<30 years old) healthy human subjects.
Methods Platelet NO synthase (NOS) activity was evaluated by l-[3H]-arginine to l-[3H]-citrulline conversion, and cGMP was determined by radioimmunoassay. Platelet expression of NOS3, phosphoserine-1177-NOS3 and soluble guanylyl cyclase (sGC) were quantified by Western blotting. Circulating monocyte–platelet aggregates (MPA) were measured by flow cytometry.
Results Basal NOS activity was similar in both groups. By contrast, whereas both albuterol and collagen stimulated platelet NOS in younger subjects, stimulation was absent in older subjects. Platelet NOS3 expression was similar in both age groups, but NOS3 serine-1177 phosphorylation was greater in younger subjects. Basal, albuterol- and collagen-stimulated cGMP, as well as sGC expression, were all greater in younger than older subjects, and within the younger group both cGMP (basal and stimulated) and sGC expression were greater in women than in men. Circulating MPA were greater in older subjects and, whilst NOS inhibition increased MPA further in both groups, it did so to a lesser extent in the older age bracket.
Conclusions These data suggest that platelet NO production and responsiveness decrease with age, and this is reflected in increased circulating MPA.
KEYWORDS Aging; Platelets; Monocyte–platelet aggregates; Nitric oxide
Abbreviations: NO, nitric oxide • NOS, nitric oxide synthase • sGC, soluble guanylyl cyclase • cGMP, cyclic guanosine-3',5'-monophosphate • cAMP, cyclic adenosine-3',5'-monophosphate • PKA, protein kinase A • PKC, protein kinase C • MPA, monocyte–platelet aggregates • AR, adrenoceptors • ER, estrogen receptors • GFP, gel-filtered platelets • PRP, platelet-rich plasma • L-NMMA, NG-monomethyl-l-arginine.
1 These authors contributed equally.
* Financial support: This study was supported by the Coronary Research Fund and the Greek Foundation for State Scholarships.