Pro‐apoptosis effects of neutrophils in mice subjected to myocardial ischemic reperfusion in vivo

Aim To determine potential mechanisms involved in PMNs′ contribution to myocardial ischemic reperfusion (MI/R). Method 32 male adult mice were randomly divided into equal four groups: Vehicle, 1400W(iNOS inhibitor), Anti‐PMNs (anti‐PMN serum, i.p., 30μl/day for 3 consecutive days prior to MI/R) and Sham group. MI/R was produced by ligating the LAD for 30min followed by 5 hours of reperfusion. Myocardial apoptotic index, caspase3, MPO activity and ONOO − formation (measured by nitrotyrosine, NT) were determined. Result 1. Compared with sham group MI/R markedly increased apoptotic index (1.02±0.16% vs. 18.01±0.06%, P <0.01), caspase3 activity (63.82±8.40 vs. 25.64±2.60μM/mg, P <0.001), MPO activity (163.31±12.95 vs. 65.52±7.66ng/mg, P <0.001) and NT content (6.8±0.67 vs.1.6±0.14nmol/g, P <0.001); 2. Both Anti‐PMNs and 1400W treatment reduced reperfusion‐induced apoptotic index, caspase3 activity and NT content; MPO activity in Anti‐PMNs group was 84.52±9.62ng/mg ( P <0.001 vs. vehicle); 3. As for the reduction of apoptosis and the formation of NT, there were no significant differences between Anti‐PMNs and 1400W group, but the MPO activity in 1400W group was much higher ( P <0.005). Conclusion PMNs contribute to MI/R‐induced apoptosis by increasing iNOS, subsequent production of ONOO − and activating pro‐apoptotic signaling pathways. Anti‐PMNs treatment may not only attenuate postischemic myocardial inflammation as previously reported, but may also protect the heart from subsequent MI/R‐induced apoptosis.