PILOT: ANGIOTENSIN RECEPTOR BLOCKER AS POTENTIAL THERAPEUTICS FOR TBI

TBI results in complex pathological reactions ¿ damage caused by the initial lesion followed by a secondary cascade involving inflammation, edema and a strong glial response. The secondary consequences of the initial injury lead to significantly larger lesion volume, worsening of neurological competence and result in an environment around the lesion that is more inhibitory to regeneration. Angiotensin II (AngII) is produced in the brain and is known to be vasoconstrictive and pro-inflammatory. The two major classes of receptors for AngII, AT1 and AT2 receptors are expressed in the CNS and often have opposing actions, AT1 receptors mediating most physiological effects of Ang II. AT1Rs are expressed on neurons and endothelial cells in the CNS, in numerous brain regions including the cortex. In addition to powerful vasoconstriction of the cerebral microvasculature, AT1R signaling also elicits strong pro-inflammatory actions in the brain, through production of reactive oxygen species, inflammatory cytokines and adhesion molecules. Ang II receptor blockers (ARBs) are specific antagonists of the AT1 receptor and are widely used FDA ¿approved drugs with limited side effects. ARBs, are potent anti-inflammatory agents in the CNS. In rodent models of stroke, treatment with ARBs lessened the lesion penumbra, decreased the number of apoptotic cells and improved neurological outcome. ARBs also have been shown to ameliorate the cognitive impairment seen after whole brain irradiation in rats. Thus, ARBS in addition to their anti-inflammatory actions appear also to be neuroprotective. We therefore hypothesize that ARBs will have efficacy in treating TBI in mice, through decreasing inflammatory sequelae, reducing the lesion penumbra, and limiting secondary neuronal cell death. The objective of this pilot proposal is therefore to examine the effects of the ARB, candesartan, on recovery from controlled cortical impact (CCI) to the cerebral cortex in mice. We will first characterize the expression of components of the Angiotensin II pathway in the CNS at specific time points after CCI injury to mice. Little is known of the response of the Angiotensin II system to TBI. However, AT1R expression is upregulated by inflammation and stress. We will therefore examine expression of the AT1 and AT2 receptors, indicative of activation of the Angiotensin II system in the sham and injured brain at 6 hours, 1, 3, 7 and 28 days after moderate CCI injury by in situ hybridization, autoradiography and immunohistochemistry. Secondly we will determine whether treatment of mice with the ARB, candesartan, after CCI injury, lessens the morphological and functional outcomes of TBI. We will implant a minipump containing candesartan or vehicle 5 hours before CCI of moderate impact. Mice will be sacrificed at 3 and 28 dpi after first assessing motor and cognitive function. Brains will then be examined for lesion volume, cell death, inflammatory markers, glial reactivity and scar formation at these different time points to assess the morphological result of treatment with candesartan. Given the strong evidence in the literature that the ARBs are beneficial to different models of neuronal injury, we anticipate that this project will show that ARBs are efficacious in treating TBI in mice. Immediate treatment with ARBs may reduce inflammation, promote neuronal survival and lessen glial scarring to allow for more successful regenerative approaches.