Liberation of vessel adherent myeloperoxidase by enoxaparin improves endothelial function

Abstract

Background Myeloperoxidase (MPO), a leukocyte-derived heme enzyme binds to the endothelium and depletes vascular nitric oxide (NO) bioavailability in animal models. Unfractionated heparins release vessel-bound MPO and increase endothelial NO bioavailability. Whether low molecular weight heparins also affect circulating MPO levels and NO dependent vasoreactivity however remains elusive. Methods and results In a randomized, double-blind, placebo-controlled trial patients with stable coronary artery disease received either 1 mg/kg enoxaparin or an equivalent volume of sodium chloride (NaCl) subcutaneously. Enoxaparin led to a significant improvement of FMD (5.51 ± 0.53% vs. 6.55 ± 0.58%, p = 0.01) accompanied by a significant increase in plasma MPO levels (2.51 [IR: 2.04–3.62] ng/ml vs. 3.70 [IR: 2.80–5.50] ng/ml; p < 0.001) whereas NaCl revealed neither a change in FMD (5.56 ± 0.67% vs. 5.34 ± 0.61%, p = ns) nor in plasma MPO levels (3.04 [IR: 2.22–4.67] ng/ml vs. 2.90 [IR: 1.95–4.32] ng/ml; p = ns). The extent of enoxaparin-induced MPO release and the improvement in endothelial function showed a good correlation ( r = 0.67, p < 0.001). Discussion This study confirms the concept that heparins improve endothelial function, an established read-out of vascular NO bioavailability, by mobilizing vessel bound MPO. These data not only support the notion of extracoagulant, anti-inflammatory properties of heparins but reinforce the concept of MPO-dependent NO oxidation as a central mechanism for regulation of vascular tone in inflammatory vascular disease. (Eudra-CT number: 2005-006113-40).