Spinal Peroxynitrite Contributes to Remifentanil-induced Postoperative Hyperalgesia via Enhancement of Divalent Metal Transporter 1 without Iron-responsive Element-mediated Iron Accumulation in Rats

Background: Hyperalgesia is one of the negative consequences following intraoperative analgesia with remifentanil. Peroxynitrite is a critical determinant in nociceptive process. Peroxynitrite inactivates iron-sulfur cluster that results in mitochondrial dysfunction and the release of iron, leading to mitochondrial iron accumulation. Iron accumulation mediated by divalent metal transporter 1 (DMT1) plays a key role in N-methyl-D-aspartate neurotoxicity. This study aims to determine whether peroxynitrite contributes to remifentanil-induced postoperative hyperalgesia via DMT1-mediated iron accumulation. Methods: Behavior testing was performed in rat model at different time points. Three-nitrotyrosine, nitrated manganese superoxide dismutase, and DMT1 with/without iron-responsive element [DMT1(+) IRE and DMT1(-)IRE] in spinal cord were detected by Western blot and immunohistochemistry. Spinal iron concentration was measured using the Perl stain and atomic absorption spectrophotometer. Hydrogen-rich saline imparting selectivity for peroxynitrite decomposition and iron chelator was applied in mechanistic study on the roles of peroxynitrite and iron, as well as the prevention of hyperalgesia. Results: Remifentanil induced thermal and mechanical hyperalgesia at postoperative 48 h. Compared with control, there were higher levels of 3-nitrotyrosine (mean +/- SD, hyperalgesia vs. control, 1.22 +/- 0.18 vs. 0.25 +/- 0.05, n = 4), nitrated manganese superoxide dismutase (1.01 +/- 0.1 vs. 0.19 +/- 0.03, n = 4), DMT1(-) IRE (1.42 +/- 0.19 vs. 0.33 +/- 0.06, n = 4), and iron concentration (12.87 +/- 1.14 vs. 5.26 +/- 0.61 mu g/g, n = 6) in remifentanil-induced postoperative hyperalgesia, while DMT1(+)IRE was unaffected. Eliminating peroxynitrite with hydrogen-rich saline protected against hyperalgesia and attenuated DMT1(-) IRE overexpression and iron accumulation. Iron chelator prevented hyperalgesia in a dose-dependent manner. Conclusions: Our study identifies that spinal peroxynitrite activates DMT1(-) IRE, leading to abnormal iron accumulation in remifentanil-induced postoperative hyperalgesia, while providing the rationale for the development of molecular hydrogen and iron-targeted therapies.