Studies of hypoxemic/reoxygenation injury: Without aortic clamping: VI. Counteraction of oxidant damage by exogenous antioxidants: N-(2-mercaptopropionyl)-glycine and catalase

Abstract

This study tests the hypothesis that antioxidants administered before reoxygenation can reduce oxygen-mediated damage and improve myocardial performance. Of 25 Duroc-Yorkshire piglets (2 to 3 weeks, 3 to 5 kg) five underwent 60 minutes of cardiopulmonary bypass without hypoxemia (control group), and five others underwent 30 minutes of hypoxemia on cardiopulmonary bypass with a circuit primed with oxygen tension about 25 mm Hg blood followed by reoxygenation on cardiopulmonary bypass (no treatment). In vitro studies were performed to obtain the optimal dosage of the antioxidants N -(2-mercaptopropionyl)-glycine and and catalase to be used in subsequent in vivo experimental studies; cardiac homogenates were incubated in 0 to 5 mmol/L concentrations of the oxidant t -butylhydroperoxide and malondialdehyde production was measured. Fifteen piglets were made hypoxemic on cardiopulmonary bypass for 30 minutes, and the antioxidants N -(2-mercaptopropionyl)-glycine at either 30 or 80 mg/kg body weight or N -(2-mercaptopropionyl)-glycine, 30 mg/kg body weight, and catalase, 50,000 U/kg body weight, were added to the cardiopulmonary bypass circuit 15 minutes before reoxygenation. Left ventricular contractility, which was expressed as end-systolic elastance, was measured by conductance catheter before hypoxemia and after reoxygenation. Myocardial antioxidant reserve capacity was determined after reoxygenation by incubating cardiac homogenates in the oxidant t -butylhydroperoxide and measuring subsequent malondialdehyde elution. The in vitro bioassay studies showed a dose-dependent reduction of lipid peroxidation with N -(2-mercaptopropionyl)-glycine, with maximal benefits of a 40% decrease and malondialdehyde elaboration occurring with N -(2-mercaptopropionyl)-glycine and catalase compared with untreated cardiac homogenates. Cardiopulmonary bypass (no hypoxemia) caused no oxidant damage or changes in contractile function after cardiopulmonary bypass. Reoxygenation without treatment raised conjugated diene levels 57%,* lowered antioxidant reserve capacity 51%,* and was associated with only 38%* recovery of contractile function ( p < 0.05 vs control). In contrast, treatment with antioxidants avoided lipid peroxidation, maintained antioxidant reserve capacity, and resulted in a dose-dependent improvement in left ventricular contractility with complete recovery occurring in N -(2-mercaptopropionyl)-glycine and catalase-treated piglets (* p < 0.05 vs no treatment). This study confirms the occurrence of hypoxemic/reoxygenation injury in immature hearts placed on cardiopulmonary bypass and shows that biochemical and functional damage can be counteracted by adding antioxidants to the cardiopulmonary bypass priming fluid. Contractile function improved in a dose-dependent manner, and oxygen-mediated damage could be avoided by mercaptopropionyl glycine/catalase treatment. In vitro studies were helpful to determine drug dosages to be used in in vivo experiments and may be useful to reduce the number of whole animal experiments required to develop optimal dosage regimens. (J T horac C ardiovasc S urg 1995; 110:1212-20)