Scavenging of hypochlorous acid and the myoglobin-derived oxidants by of cardioprotective agent mercaptopropionylglycine

Mercaptopropionylglycine (MPG) has a marked cardioprotective action in several model systems of ischaemia-reoxygenation injury. Suggested mechanisms of action include scavenging of hydroxyl radical and the hypochlorous acid and reacting with an oxidant formed by reaction of myoglobin with H₂O₂, thereby slowing lipid peroxidation stimulated by myoglobin-H₂O₂ mixtures. This oxidant seems not to be singlet O₂ or hydroxyl radical. Studies in vitro show that scavenging of hypochlorous acid is a feasible mechanism of cardioprotective action for MPG in vivo in ischaemia/reperfusion systems to which neutrophil-mediated injury contributes. However, the poor ability of MPG to inhibit lipid peroxidation stimulated by myoglobin/H₂O₂ mixtures and its ability to increase iron ion release from myoglobin in the presence of a large excess of H₂O₂, suggests that MPG is unlikely to protect the myocardium by interfering with oxidants produced by the myoglobin-H₂O₂ system.