Developing an adjunct therapy to mechanical thrombectomy in a murine model of stroke ischaemia reperfusion injury

Abstract

Mechanical thrombectomy (MT) is increasingly used to treat ischaemic stroke as it allows for more rapid and complete reperfusion of the ischaemic tissue compared to recombinant tissue plasminogen activator (rtPA) alone. The advancements in imaging techniques, together with MT, have extended the therapeutic window of reperfusion therapy and have enhanced patient outcomes in ischaemic stroke. However, despite these improvements, brain infarction and damage following MT are exacerbated by ischaemia-reperfusion (IR) injury during reperfusion of the ischaemic tissue. Therefore, an adjunct therapy to MT that decreases IR injury should enhance patient outcomes. One of the main drivers of IR injury is the accumulation of the tricarboxylate acid (TCA) cycle intermediate succinate during ischaemia and its rapid oxidation during reperfusion by succinate dehydrogenase (SDH). This drives reverse electron transport (RET) via complex I of the mitochondria to generate harmful reactive oxygen species (ROS) in a process known as RET-ROS. The SDH inhibitor disodium malonate (DSM) has been reported to enter cells via monocarboxylate transporter 1 (MCT1) to inhibit RET-ROS and reduce IR injury. The uptake and efficacy of DSM can be enhanced by low pH, which increases the proportion of its monocarboxylate form, the substrate for MCT1. Therefore, the main aim of this thesis is to develop locally administered acidified DSM (aDSM) as an adjunct therapy to MT using the murine transient middle cerebral artery occlusion model (tMCAO). In this thesis, I have adapted the tMCAO to allow local drug administration during reperfusion via an intra-arterial polyimide-based microcatheter. I show that this novel model with the intra-arterial catheter is robust and comparable to the traditional model. Using this model, I characterised the uptake and efficacy of intravenous tail-vein administration and local intra-arterial administration of DSM and aDSM against stroke IR injury. I showed that both local administration and acidification of DSM independently enhanced uptake and efficacy against stroke IR injury. I further characterised the efficacy of locally administered aDSM using clinically translatable methods of magnetic resonance imaging (MRI) and neurological scoring, showing that aDSM (160 mg/kg; pH 6.0) decreased infarct volume by 65 %, improved neurological outcomes, and was compatible with rtPA. Lastly, I examined the role of RET-ROS in IR injury by showing that the ND6-P26L mouse model, which cannot catalyse RET-ROS, exhibited a natural protection (≈65 %) against stroke IR injury. Furthermore, I also elucidated the mechanism of aDSM protection by demonstrating a reduction in oxidative damage following stroke IR injury.