Mitochondrial Metabolism in Ischaemia Reperfusion Injury
Ischaemia reperfusion (IR) injury is caused by the re-introduction of oxygenated blood flow to tissues after a period of ischaemia. It is an inevitable consequence of organ transplantation, where its severity contributes to reduced levels of graft function and survival. There are no clinically approved pharmacological therapies available to ameliorate the effects of IR injury in organ transplantation or other ischaemic pathologies. Many candidate drugs found to be promising in pre-clinical models fail to show efficacy in humans. Despite this, improving our understanding of the underlying pathophysiological mechanisms has supported the development of rational therapeutic approaches. Mitochondria are integral to IR injury, and the respiratory complex succinate dehydrogenase (SDH) has been identified as a new therapeutic target. The mitochondrial metabolite succinate accumulates during ischaemia, before being rapidly oxidised by SDH upon reperfusion, producing reactive oxygen species (ROS), and leading to oxidative damage and cell death. The aim of this thesis was to determine whether treatment with disodium malonate (DSM), a competitive inhibitor of SDH, reduces mitochondrial ROS production during reperfusion, thereby ameliorating IR injury in translational models. In vivo mouse and pig kidney models of IR injury were characterised in detail, and a qualitative comparison confirmed similar global metabolic changes. In addition, succinate metabolism was found to be highly conserved in pig and human models involving ex vivo perfusion of isolated kidneys. Mass spectrometry imaging showed that succinate metabolism was similar in the different anatomical compartments of the kidney and was a suitable method for detecting mitochondrial hydrogen peroxide production using the ratiometric probe, MitoB. Treatment with DSM prior to IR injury reduced oxidative damage and cell death while preserving kidney function. Meanwhile, DSM treatment of healthy tissues resulted in widespread changes to the abundance of intermediates in key metabolic pathways, significantly altered expression of genes controlling important cellular processes, and increased serum concentration of pro-inflammatory cytokines. These data show that DSM is a promising novel therapeutic for ameliorating IR injury, likely due to its effects on succinate metabolism, which is highly conserved between animal and human models.
metabolism, mitochondria, ischaemia reperfusion injury, ischemia reperfusion injury, succinate dehydrogenase, organ transplantation, transplant, metabolomics
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