Summary
Essential thrombocythaemia (ET) and polycythaemia vera (PV) are characterised by a
high incidence of thrombotic complications due to highshear stress of the vessel wall,
blood hyperviscosity and hypoxaemia, all factors responsible for chronic endothelial
dysfunction and platelet and leukocyte activation. We evaluated the activation status
of vascular cells in 18 consecutive ET and 14 PV patients by measuring the plasma
levels of the nitric oxide derivatives (NOX) (i.e. nitrites and nitrates) and of soluble selectins of platelet (P-selectin),
endothelial cell (P-selectin and E-selectin) and leukocyte (L-selectin) origin. The
effect of hydroxyurea (HU) therapy on these parameters was also investigated. NOX were significantly (p<0.01) increased in ET patients treated with HU (11.5 ± 2.6
nM) compared to non-HU treated ET (1.41 ± 0.3 nM) and to controls (4.78 ± 2.49 nM).
Multivariate analysis confirmed HU therapy as an independent predictor of higher NOX levels in ET. In addition, NOX significantly correlated with haematocrit. Plasma P-selectin was significantly elevated
in ET (350 ± 40 ng/106 platelets) and PV (482 ± 53 ng/106 platelets) patients compared to controls (120 ± 8 ng/106 platelets). In PV, also
E-selectin (23.8 ± 4.2 ng/ml) was significantly increased compared to controls (11.2
± 1.1 ng/ml; p<0.01). P-selectin was significantly correlated to platelet (R=0.33;
p=0.01) and leukocyte count (R=0.6; p=0.000), while E-selectin (R=0.34; p=.014) and
sL-selectin (R=0.3; p=0.03) were correlated with leukocyte count only. In the multivariate
analysis, NOX predicted increased levels of E-selectin in ET, but not in PV patients. Our data
demonstrate that ET and PV are characterised by an altered pattern of soluble selectins
and NOX. HU-mediated increase of NOMX levels could represent an additional antithrombotic mechanism of this drug.
Keywords
Nitric oxide - selectins - essential thrombocythemia - polycythemia vera - Hydroxyurea