PEG-SOD and myocardial antioxidant status during ischaemia and reperfusion: dose-response studies in the isolated blood perfused rabbit heart.

Abstract We have previously shown that the polyethylene glycol conjugated superoxide dismutase (SOD), which has a plasma half-life of more than 24 h, protects the blood perfused rabbit heart against injury during ischaemia and reperfusion. However, the profile for the dose-dependency of protection was bell-shaped with loss of efficacy below 6000 and above 30 000 U/kg. In the present study, isolated rabbit hearts, perfused with blood from support rabbits, were subjected to a 2 min infusion with St Thomas' Hospital cardioplegic solution followed by 60 min of global ischaemia (37°C) and 60 min of reperfusion. PEG-SOD was administered 1 h or 12–24 h before ischaemia. We assessed the effect of PEG-SOD on ischaemia- and reperfusion-induced changes in: (i) the tissue content of reduced glutathione (GSH), oxidized glutathione (GSSG) and malondialdehyde (MDA) and (ii) the activity of CuZn-SOD, Mn-SOD and glutathione peroxidase and reductase (GPD and GRD). Ischaemia and reperfusion reduced tissue GSH content by 70% and increased GSSG content by 400% (from their fresh aerobic values of 13.1.9 and 0.09 ± 0.01 nmol/mg protein, respectively). PEG-SOD, given intravenously at various doses to donor and support rabbits 1 h or 12–24 h before ischaemia, protected against these changes with a bell-shaped dose-response relationship. Thus, with 0, 3000, 6000, 12 000, 30 000 and 60 000 U/kg, GSH content was 4.1 ± 0.4, 4.8 ± 0.4, 8.5 ± 0.5, 12.3 ± 1.6, 12.3 ± 1.6 and 5.0 ± 0.5 nmol/mg protein in the 1 h pretreatment group and 4.1 ± 0.4, 4.2 ± 0.5, 10.4 ± 1.5, 11.2 ± 1.1, 11.4 ± 0.7 and 4.7 ± 0.6 nmol/mg protein in the 12–24 h pretreatment group (means ± s.e.m. ). For GSSG the corresponding values were 0.36 ± 0.04, 0.34 ± 0.03, 0.12 ± 0.01, 0.12 ± 0.01, 0.11 ± 0.01 and 0.41 ± 0.03 nmol/mg protein for the 1 h group and 0.36 ± 0.04, 0.35 ± 0.02, 0.15 ± 0.01, 0.12 ± 0.01, 0.11 ± 0.01 and 0.34 ± 0.02 nmol/mg protein for the 12–24 h group. Ischaemia and reperfusion had no effect on tissue MDA content or CuZn-SOD, GDP and GRD activity, and in general, PEG-SOD also lacked significant effect on any of these variables at any dose studied. However, Mn-SOD activity was severely reduced by ischaemia and reperfusion (from 42 ± 7 U/mg protein in fresh aerobic controls to 6 ± 1 U/mg protein at the end of reperfusion). PEG-SOD at doses of 6000, 12 000 and 30 000 U/kg prevented this loss and maintained enzymic activity in the normal range. In conclusion, PEG-SOD pretreatment, administered 1 h or 12–24 h before ischaemia, protects the heart against deleterious changes in antioxidant status induced by ischaemia and reperfusion. The dose-response relationship is bell-shaped and closely reflects the functional protection seen in previous studies.