Purpose: The upregulation of spinal NMDA receptor is a crucial mechanism in remifentanil-induced hyperalgesia (RIH). Wnt3a/β-catenin pathway plays an important role in neuropathic pain. We hypothesized that wnt3a inhibitor (iwp-2) could downregulate the expression of NR₂B subunit in NMDA receptor, in order to relieve RIH.
Materials and Methods: The study has 2 phases. The phase 1 study is designed by different doses of iwp-2 groups to create an appropriate iwp-2 dose used in RIH alleviation. The phase 2 study is designed to prove that the wnt3a inhibitor could downregulate the activation of the NR₂B to inhibit RIH in rats. Thermal hyperalgesia (PWTL) and mechanical allodynia (PWMT) were evaluated after RIH. The area under the PWTL and PWMT curves (AUC) were calculated. The amount of activated NR₂B subunit, c-fos, NF-κB, β-catenin, wnt3a and p-GSK-3β (Ser9) were detected in the lumbar spinal cord.
Results: Remifentanil infusion could induce overexpression of β-catenin and wnt3a in rats. Iwp-2 (60μM, 120μM, 180μM) could dose-dependently inhibit thermal hyperalgesia and mechanical allodynia in rats. In phase 2 study, both NR₂B subunit antagonist Ro25-6981 and iwp-2 decreased the amount of activated NR₂B, enhanced p-GSK-3β (Ser9), reduced β-catenin, c-fos and NF-κB in the lumbar spinal cord (p < 0.001). In comparison with the group iwp-2, the group of Ro25-6981 had more benefit in reversing hyperalgesia, including higher AUC value of PWTL (p = 0.022) and PWMT (p = 0.035).
Conclusion: Remifentanil exposure could induce overexpression of wnt3a and enhance the production of β-catenin in the spinal dorsal horn. Inhibition of wnt3a response was capable of attenuating RIH in alleviating hyperalgesia-related behavioral parameters, as well as reducing overexpression of c-fos, NF-κB, NR₂B in spinal dorsal horn.
Keywords: remifentanil, hyperalgesia, iwp-2, NR₂B, wnt3a/β-catenin