We have previously documented that generation of the potent reactive nitrogen species (RNS) peroxynitrite (PN) is responsible for oxidative damage by lipid peroxidation (LP) and protein modification (carbonylation and tyrosine nitration) to mitochondrial and other cellular elements during the first 72 hrs after traumatic brain injury (TBI). The PN-mediated oxidative damage leads to brain mitochondrial dysfunction and ultimately failure. As a consequence of oxidative compromise of mitochondrial function including calcium (Ca++) buffering), posttraumatic intracellular Ca++ overload is exacerbated leading to calpain-mediated cytoskeletal degradation, neurodegeneration and neurological impairment. We have preliminarily shown that treatment with the potent LP inhibitor U-83836E, with the LP-derived lipid aldehyde 4-hydroxynonenal (4-HNE) scavenger phenelzine or with the mitochondrial permeability transition inhibitor cyclosporine (CsA) can partially attenuate posttraumatic brain LP damage, mitochondrial dysfunction and calpain-mediated cytoskeletal damage in a mouse TBI model. Most importantly, the window for this effect is at least 12 hrs post-injury. However, our preliminary results show only a partial attenuation of post-injury LP-related neural damage'even when any of these antioxidant compounds is individually administered after injury. This partial neuroprotective effect strongly points to the logic of an antioxidant neuroprotective strategy that combines either two or all three of these mechanistically complimentary antioxidant compounds to achieve a greater degree of neuroprotection. Therefore, the overall goal of the proposed experiments is to explore the hypothesis that interrupting post-traumatic secondary LP oxidative damage at multiple points will produce a quantitatively greater neuroprotective effect with less variability that will have a greater chance of translational success in future TBI clinical trials. The combination approach should not only increase the maximal neuroprotective effect, but may also prolong the therapeutic window for inhibition of secondary brain injury after TBI.
This project will examine the potentially greater benefits that might be obtained in the rat controlled cortical impact traumatic brain injury model when multiple neuroprotective compounds that target oxidative secondary injury mechanisms are administered together. Specifically, we will test a combination multi-mechanistic antioxidant treatment strategy combining two or three of the following mechanistically complimentary antioxidant compounds: 1) the lipid peroxidation-inhibiting drug U-83836E, 2) the commercially available compound phenelzine that scavenges the neurotoxic lipid peroxidation-derived lipid aldehyde 4- hydroxynonenal (4-HNE) and 3) the extensively demonstrated mitochondrial protective compound cyclosporine A(CsA) which reduces post-TBI mitochondrial permeability transition and free radical leakage. After determining the best neuroprotective dose, optimal treatment regimen and therapeutic efficacy window of each compound, pharmacologically-optimized dosing regimens of each of the compounds will be compared in a single experiment. This will be followed by the testing of the combination effectiveness of two (U-83836E + phenelzine, U-83836E + CsA, phenelzine + CsA) or all three (U-83836E + phenelzine + CsA).