Liberation of vessel adherent myeloperoxidase by enoxaparin improves endothelial function

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.

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).

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).