Abstract 1120: Ischemia-Induced Protein Modifications That Occur Independently of Reactive Oxygen Species in Stunned Myocardium
A brief period of ischemia followed by timely reperfusion may lead to prolonged, yet reversible, contractile dysfunction (‘myocardial stunning’). Damage to the myocardium can occur during ischemia, but mainly takes place during reperfusion, where a massive release of reactive oxygen species (ROS) occurs. Utilizing two-dimensional gel electrophoresis (2-DE) and mass spectrometry, 57 protein spot changes were associated with brief ischemia / reperfusion (I/R; 15 mins I, 60 mins R; 15I/60R) injury in a rabbit model. When treated with the ROS scavenger N-(2-mercaptopropionyl) glycine (MPG) (15I/60R+MPG) 37 of these 57 protein spots that had been altered during 15I/60R remained at control levels. All observed changes to contractile proteins, including myosin light chain 2 and troponin C , were prevented by the addition of MPG. To further investigate the individual effects of ischemia and reperfusion, 2-DE gels generated from rabbit myocardium subjected to brief ischemia alone (15I/0R), revealed alterations to 33 protein spots, including 18 of the 20 seen in both 15I/60R- and 15I/60R+MPG-treated tissue. When supplemented with MPG (15I/0R+MPG), ischemia-specific damage was further reduced to 21 spot changes, representing 9 distinct proteins, remaining altered despite the presence of the ROS scavenger. This ischemia-specific/ROS-independent protein damage comprised proteins involved in energy metabolism (lactate dehydrogenase β-enolase and ATP synthase α), redox regulation (NADH ubiquinone oxidoreductase 30kDa and 51kDa, and glutathione S-transferase Mu), and stress response (Hsp27 and 70, and deamidated α B-crystallin). We conclude that contractile dysfunction associated with myocardial stunning is predominantly caused by ROS damage at the onset of reperfusion, but that specific ROS-independent damage also occurs during ischemia. Calcium overload during ischemia may mediate this ischemia-specific/ROS-independent protein damage, and these modifications may be indicative of early myocardial injury.