Carbon monoxide-releasing molecule 3 inhibits myeloperoxidase (MPO) and protects against MPO-induced vascular endothelial cell activation/dysfunction

Polymorphonuclear leukocyte (PMN)-derived myeloperoxidase (MPO) contributes to the pathophysiology of numerous systemic inflammatory disorders through: (1) direct peroxidation of targets and (2) production of strong oxidizing compounds, e.g., hypohalous acids, particularly hypochlorous acid, which furthers oxidant damage and contributes to the propagation of inflammation and tissue injury/dysfunction. Carbon monoxide-releasing molecules (CORMs) offer potent anti-inflammatory effects; however, the mechanism(s) of action is not fully understood. This study assessed the potential of MPO activity inhibition by a water-soluble CORM, CORM-3. To this end, we used in vitro assays to study CORM-3-dependent modulation of MPO activity with respect to: (1) the inhibition of MPO's catalytic activity generally and (2) the specific inhibition of MPO's peroxidation and halogenation (i.e., production of hypochlorous acid) reactions. Further, we employed primary human umbilical vein endothelial cells (HUVECs) to investigate MPO-dependent cellular activation and dysfunction by measuring intracellular oxidant stress (DHR-123 oxidation) and HUVEC permeability (flux of Texas red-dextran), respectively. The results indicate that CORM-3 significantly inhibits MPO activity as well as MPO's peroxidation and hypohalous acid cycles specifically (p<0.05 vs uninhibited MPO). In addition, CORM-3 significantly decreases PMN homogenate- or rhMPO-induced intracellular DHR-123 oxidation in HUVECs and rhMPO-induced HUVEC monolayer permeability (p<0.05 vs untreated). In all assays the inactivated CORM-3 was significantly less effective than CORM-3 (p<0.05). Taken together our findings indicate that CORM-3 is a novel MPO inhibitor and mitigates inflammatory damage at least in part through a mechanism involving the inhibition of neutrophilic MPO activity.