Overexpression of wild-type human SOD1 in mice prevents myocardial reperfusion injury

While superoxide derived free radicals are generated in ihe postischemic heart and are important mediator of reperfusion injury, there is controversy regarding whether genetic engineering increased expression ol the superoxide metabolizing enzyme copper zine superoxide dismutase (SOD1) can prevent cellular anjury. Therefore, studies were performed in isolated hearts from transgenic mice expressing increased levels of wild-type human SOD1 (TG) or in nontransgenic controls (NT) with normal SOD levels (N=16/grp). Measurements of contractile function, oxygen free radicals (OFR), and high energy phosphates (HFP) were performed in hearts before and after 30 min of 37°C ischemia (1) followed In 45 min reperfusion (R). OFR generation and HEP were measured using electronic paramagnetic resonance (EPR) spin trapping (using 40mM DMPO) and ³¹P nuclear magnetic resonance (NMR). respectively. Contractile function and infarction were studied in parallel. NT hearts exhibited a typical burst generation of OFR in the first 2 min of reflow, with more than 10 fold rise above preischemic levels, while no OFR was seen in TG hearts which had 6-8 fold increased expression of SOD1 (measured by Western Blot). After 45 min of R, TG hearts exhibited much higher recovery of contractile function with 21.9±.04% vs 10.9 ±0.3% recovery of rate pressure product (p≤0.05). This correlated with higher recovery of ATP (61.8±7.4% vs 29.6±3.1%, p≤0.()5) and phosphocreatine (70.9±8.9% vs 51.7±4.2%, p≤0 05). Myocardial infarction after 45 min reflow was measured by TTC staining. In TG hearts much less infarction was seen than in NT hearts. 14.2±1.1% vs 30.77±2.8%, p≤0.01. Thus, genetic engineering of increased intrazellular SOD expression prevents postischemic free radical generation and confers resistance to myocardial reperfusion injury.