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Title: Targeting mitochondrial ROS production in kidney transplantation
Author: Beach, Timothy Elliott
ISNI:       0000 0004 9348 1041
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2020
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Ischaemia reperfusion injury (IRI) is an inevitable consequence of transplant practices but is associated with reduced levels of graft function and survival. In addition, concerns regarding the severity of IRI has restricted the greater use of organs from the available donor pool. Critically, no pharmacological therapies currently exist to ameliorate the effects of IRI in organ transplantation (or other IRI-related pathologies), partly due to an incomplete understanding of the underlying pathophysiology. Recently, a specific mechanism of mitochondrial reactive oxygen species (ROS) production, thought to initiate many of the downstream pathways resulting in IRI, has been described. This mechanism has identified a number of new therapeutic targets within mitochondria, including the respiratory complex succinate dehydrogenase (SDH). The aim of this thesis was to determine whether malonate ester prodrugs, which competitively inhibit SDH, may reduce mitochondrial ROS production and ameliorate IRI in models of kidney transplantation. Herein, I show that the metabolic changes required for mitochondrial ROS production on reperfusion, including succinate accumulation and the depletion of adenine nucleotides, occur in grafts retrieved from both DBD and DCD donors, despite differences in their exposure to warm ischaemia. This may partly relate to difficulties in efficiently cooling organs and suggests grafts from both donor types may benefit from therapies aimed at reducing mitochondrial ROS production. I describe a translational model of kidney transplantation in the pig and human as well as a model of renal IRI in the mouse. I show the mitochondrial ROS probe, MitoB, may be limited in its ability to accurately quantify the burst of mitochondrial ROS production that occurs during IRI in the kidney; however mitochondrial ROS production may instead be inferred indirectly in mouse, pig and human models by comparing the metabolic changes that occur on reperfusion to those previously described to drive mitochondrial ROS production in vitro. In addition, I identify key markers of oxidative damage, cell death and kidney function in the mouse, pig and human and subsequently show malonate ester prodrugs administered at reperfusion (but not prior to ischaemia) may reduce IRI in the mouse. Finally, I present pilot data in the pig providing important dosing and timing information for the use of malonate ester prodrugs in this model. Further work is needed to determine whether malonate ester prodrugs may inhibit mitochondrial ROS production in kidney transplantation; however, this thesis has provided important inroads into the use of these compounds in a transplant setting as well as characterising a number of translational models that may pave the way to their use in future clinical trials.
Supervisor: Saeb-Parsy, Kourosh Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Ischaemia reperfusion injury ; Transplantation ; Succinate ; Mitochondria ; Kidney ; Malonate ; reactive oxygen species