Arteriovenous malformation endothelium and responses to radiation

Cerebral arteriovenous malformations (AVMs) are congenital lesions that cause brain haemorrhage leading to death or permanent neurological disability in children and young adults. Treatment options to prevent haemorrhage include surgery, radiosurgery and embolisation. Depending on the size and location of the lesion, over one-third of AVMs cannot be treated safely with current options. Therefore, there is a need for a new treatment. It is proposed that vascular targeting could be a novel effective therapy for AVMs that are currently untreatable. An antibody attached to an effector molecule such as thrombin or tissue factor may be targeted at a specific molecule expressed in AVM vessels to create intravascular thrombosis. A better understanding of the AVM endothelial molecular biology is thus required for identifying the best candidates for vascular targeting in AVMs. Vascular targeting has been applied successfully in the treatment of cancer because of the significant differences between the tumour and normal vasculatures. This however is not the case in AVMs. It is proposed that radiosurgery can ‘prime’ AVM endothelial cells by stimulating them to express certain proteins, which could then be targeted. This thesis aims at identifying molecular changes in the endothelial cells exposed to irradiation for the development of a potential vascular target. To accomplish this, radiation-induced molecular changes were investigated in human brain microvascular endothelial cells as well as in animal models of AVM. Furthermore, endothelial microparticles were characterised to evaluate molecular changes in human AVMs. Previous in vitro studies on mouse brain endothelial cells have shown that irradiated cells express CD51, CD109 and BMP3 protein markers. One of the aims of this project was to determine the localisation of these three molecules in the endothelium of AVM animal models that were exposed to irradiation and also to identify the proteins expressed in human cerebral microvascular endothelial cells in response to radiation. Studies in rat models of AVM showed increased abundance of BMP3 in AVM vessels on day 21 post-irradiation. In vitro studies showed talin to have increased relative abundance in LC/MS/MS analysis, increased band intensity in western blot analysis and increased fluorescent intensity in immunofluorescence analysis. These results add to our understanding of AVM endothelial responses to radiation. BMP3 and talin are promising protein markers for AVM vascular targeting. Further work is required to determine whether these are clinically viable and effective targets.