Inhibition of the malate–aspartate shuttle by pre-ischaemic aminooxyacetate loading of the heart induces cardioprotection

Abstract

Preserved mitochondrial function is essential for protection against ischaemia–reperfusion (IR) injury. The malate–aspartate (MA) shuttle constitutes the principal pathway for transport of reducing cytosolic equivalents for mitochondrial oxidation. We hypothesized that a transient shut-down of the MA-shuttle by aminooxyacetate (AOA) during ischaemia and early reperfusion modulates IR injury by mechanisms comparable to ischaemic preconditioning (IPC). Isolated perfused rat hearts exposed to 40 min global no-flow ischaemia were studied in: (i) control, (ii) pre-ischaemic AOA (0.1 mM), (iii) IPC, and (iv) AOA+IPC hearts. IR injury was evaluated by infarct size and haemodynamic recovery. Tracer-estimated glucose oxidation and metabolic changes in glycogen, lactate, pyruvate, tricarboxylic acid (TCA) cycle intermediates, and ATP degradation products were measured. The effects of AOA on complex I respiration and reactive oxygen species (ROS) production were examined in isolated rabbit mitochondria. Treatment with AOA, IPC, or AOA+IPC induced significant infarct reduction; 28 ± 6, 30 ± 3, and 18 ± 1%, respectively, vs. 52 ± 5% of left ventricular (LV) mass for control (P < 0.01 for all). LV-developed pressure improved to 60 ± 3, 63 ± 5 and 53 ± 4 vs. 31 ± 5 mmHg (P < 0.01 for all) after 2 h reperfusion. Pre-ischaemic AOA administration inhibited glycolysis and increased glucose oxidation during post-ischaemic reperfusion similar to IPC, and suppressed complex I respiration and ROS production in the non-ischaemic heart. Changes in lactate, pyruvate, TCA intermediates, and ATP end products suggested an AOA inhibition of the MA-shuttle during late ischaemia and early reperfusion. Inhibition of the MA-shuttle during ischaemia and early reperfusion is proposed as a mechanism to reduce IR injury.