Effect of aspirin on constitutive nitric oxide synthase and the biovailability of NO

Introduction: Aspirin decreases the activity of iNOS and the formation of prostanoids. Constitutive nitric oxide synthase (cNOS) is present in endothelial cells, platelets, leukocytes and neurons, yet no data are available on the effect of aspirin on cNOS and the bioavailability of NO produced by this enzyme. Materials and methods: Human umbilical vein endothelial cells (HUVECs), rat adrenal gland pheocromocytoma cells (PC-12) and human platelets were incubated with different aspirin concentrations. The kinetics of NO, O-2(-) and ONOO- release were measured simultaneously in single cells or platelet suspensions using tandem electrochemical nanosensors. The NO, O-2(-) and ONOO- release from cells and platelets was stimulated with calcium ionophore and collagen, respectively. cNOS expression was estimated by Western blot analysis. Results: Incubation of HUVECs and PC-12 with 10(-5) mol/l of aspirin increased cNOS expression by 70 +/- 7% and 50 +/- 5, respectively. However, the NO concentration increased only by 33% in HUVECs incubated with the same aspirin concentration. Incubation of HUVECs with aspirin also increased the O-2(-) and ONOO- production. Therefore the bioavailability of NO increased only slightly in endothelium and did not reflect the increase in eNOS. This was in contrast to platelets, where maximal NO bioavailability almost doubled after incubation with aspirin. Conclusions: Aspirin did not have a significant effect on the NO bioavailability in endothelial cells. However, aspirin highly improved the NO production in platelets. The high NO production in platelets may counteract the effect of thromboxane, inhibit platelet aggregation, and compensate for the reduction of prostacycline concentration by aspirin. (C) 2003 Elsevier Ltd. All rights reserved.