Effect of an Acid-sensing Ion Channels Inhibitor on Pain-related Behavior by Nucleus Pulposus Applied on the Nerve Root in Rats

Study Design. Controlled, interventional animal study. Objective. To examine the effect of an inhibitor of acid-sensing ion channel 3 (ASIC3) on pain-related behavior induced by application of the nucleus pulposus (NP) onto the dorsal root ganglion (DRG) in rats. Summary of Background Data. ASIC3 is associated with acidosis pain in inflamed or ischemic tissues and is expressed in sensory neurons and NP cells. The ASIC3 inhibitor, APETx2, increases the mechanical threshold of pain in models of knee osteoarthritis or postoperative pain. However, the efficacy of APETx2 for pain relief in the NP application model remains unknown. Methods. Autologous NP was applied to the left L5 nerve root of 183 adult female Sprague-Dawley rats. The DRGs were treated with NP plus one of the following four treatments: saline solution (SM), low (0.01 mu g: LD), medium (0.1 mu g: MD), or high dose (1.0 mu g: HD) of APETx2. Behavioral testing was performed to investigate the mechanical withdrawal threshold using von Frey hairs. Expression of nerve growth factor, hypoxia-inducible factor-1 alpha (HIF1 alpha), activating transcription factor-3, and ionized calcium-binding adaptor molecule-1 was evaluated using immunohistochemistry. Statistical differences among multiple groups were assessed using the Steel test, the Tukey-Kramer test, and the Dunnett test. P < 0.05 were considered significant. Results. The thresholds in the HD group were higher than those in the SM group at Days 14 and 21 (P< 0.05). In the MD group, the threshold was higher than in the SM group at Day 14 P< 0.05). High doses of APETx2 reduced the expression of HIF1 alpha after Day 14 compared with the SM group ( P< 0.05). Conclusion. APETx2 significantly improved pain-related behavior in a dose-dependent manner. APETx2 may inhibit ASIC3 and partly inhibit Nav1.8 channels. This ASIC3 channel inhibitor may be a potential therapeutic agent in early-stage lumbar disc herniation.