Antioxidant/Calpain Inhibitor Combination Strategy in Acute SCI

Two of the best validated secondary injury mechanisms in the context of traumatic spinal cord injury (SCI) are reactive oxygen species-induced oxidative damage and calpain-mediated proteolytic degradation. In regards to the former mechanism, the only approved pharmacological therapy for acute SCI in humans is high dose treatment with glucocorticoid steroid methylprednisolone which has been shown to largely protect the injured spinal cord via inhibition of post-traumatic oxygen radical-induced lipid peroxidation. Although the effects of methylprednisolone are modest, the drug's demonstrated effectiveness in controlled clinical trials provides evidence that inhibition of oxidative damage mechanisms is a promising therapeutic approach. Recent work has shown that the reactive oxygen species peroxynitrite may be a key player in secondary oxidative damage in the injured spinal cord. Accordingly, Aim 1 of the current proposal will involve an examination of the neuroprotective and behavioral recovery-promoting effectiveness of two peroxynitritetargeted compounds in a rat severe contusion spinal cord injury model: penicillamine which can stoichiometrically scavenge peroxynitrite and the nitroxide antioxidant tempol which we have demonstrated can catalytically scavenge peroxynitrite-derived oxygen radicals. Preliminary studies have documented the ability of tempol to inhibit oxidative damage in the contused rat spinal cord and to improve neurological recovery and spinal tissue sparing. In Aim 2, we will investigate the neuroprotective and behavioral recovery-promoting effects of inhibition of calpain-mediated secondary damage using two newer calpain inhibitors which have improved cell permeability and blood-spinal cord barrier penetrability. The first of these is A-705253. The second is actually a dual inhibitor of calpain and oxygen radical-induced lipid peroxidation, Ipsen Compound 6d-08. In each of the Aim 1 and 2 evaluations, we will determine the best compound, the best dose, the optimum treatment duration and the therapeutic window in regards to decreasing oxidative and calpain-mediated spinal tissue damage, improvement of neurological recovery and spinal cord tissue sparing. Finally, in Aim 3, we will investigate the expected additive, or possibly synergistic, effects of combining the complimentary therapeutic approaches of peroxynitrite scavenging and calpain inhibition. In designing these experiments, we will take the best compound, dose and treatment duration from Aims 1 and 2 and look at whether their combined administration leads to greater neuroprotective effects than either compound alone. In this Aim, we will compare the effects of early administration of the two together as well as their combined effects when treatment is delayed to their maximal therapeutic windows determined in Aims 1 and 2. Finally, we will compare the effects of combined therapy after moderate and severe levels of SCI. These experiments have excellent potential for translation into future clinical trials in human SCI.