Neuropathic pain is often resistant to standard treatment protocols for pain and thus represents a significant unmet medical need. We recently found that the ubiquitin-proteasome system (UPS) may play a significant role in the expression of experimental neuropathic pain. Spinal administration of epoxomicin, a proteasome inhibitor, prevented behavioral signs of neuropathic pain. As the UPS is known to be a critical component leading to the biosynthesis of dynorphin we hypothesize that inhibition of the UPS may prevent experimental neuropathic pain, in part, by preventing the upregulation of spinal dynorphin that follows peripheral nerve injury. We had previously shown that approaches which interfere with the production or activity of spinal dynorphin attenuate neuropathic pain behaviors. We also hypothesize that epoxomicin can reverse already-established neuropathic pain, and that such reversal of the pain state will be accompanied by a normalization of spinal dynorphin levels. These hypotheses will be tested by first establishing whether UPS inhibitors can prevent or reverse experimental neuropathic pain (Aim 1). We will also establish the optimal treatment protocol regarding dosing schedule, dose and route of administration of epoxomicin. We will also test our hypothesis by examining spinal dynorphin expression at several time points during and after the course of epoxomicin treatments in order to determine if there is a temporal correlation between the reversal of neuropathic pain behaviors and normalization of spinal dynorphin content (Aim 2). Further, we will determine if a UPS inhibitor can normalize the characteristics of nerve-injury induced changes in cells from the dorsal root ganglia, whether such normalization is consistent with the time-course of epoxomicin activity and whether these effects might be permanent. Permanent modification of pain behavior and associated nerve injury-induced neurochemical changes would provide evidence of disease-modification . These studies will characterize the potential importance of UPS inhibition as a therapeutic approach for the treatment of neuropathic pain and provide a possible mechanistic link to spinal dynorphin activity. As most clinical conditions of neuropathic pain are treated in the post-injury (i.e., maintenance) stage, such information may allow approaches to limit or reverse the pathological actions of dynorphin to maintain neuropathic pain. UPS inhibitors are currently in clinical development for other applications. Thus, the proposed experiments are significant in that they may lay the groundwork for the development of a novel therapeutic strategy for neuropathic conditions, offering hope for treatment of neuropathic pain and perhaps ultimate disease modification. ? ? ?
| Ossipov, Michael H; Bazov, Igor; Gardell, Luis R et al. (2007) Control of chronic pain by the ubiquitin proteasome system in the spinal cord. J Neurosci 27:8226-37 |
