MPO and endothelial dysfunction: MPO is an important cause for endothelial dysfunction via production of oxidants, particularly hypochlorous acid (HOCl), hypothiocyanous acid (HOSCN), and nitrogen dioxide radical (• NO2), depletion of nitric oxide (NO) due to NO oxidase activity of MPO and non-catalytic biological activities, or cytokine-like proinflammatory effects [102].