Annexin 1 inhibits remifentanil-induced hyperalgesia and NMDA receptor phosphorylation via regulating spinal CXCL12/CXCR4 in rats.

Chemokines related neuroinflammation and N-methyl-d-aspartate receptor (NMDAR) mediated nociceptive transmission are pivotal determinants in the pathogenesis of opioid-induced hyperalgesia (OIH), but little is known about specific mechanism and treatment. Chemokine CXCL12 with its receptor CXCR4 is implicated in different pathological pain, moreover, neurotoxicity of CXCL12 is associated with NMDAR activation. Recent studies recapitulate the anti-nociception of Annexin 1 (ANXA1) in inflammatory pain. This study examined whether ANXA1 prevented remifentanil-caused OIH through modulating CXCL12 and NMDAR pathway in rats. Acute exposure to remifentanil induced mechanical allodynia and thermal hyperalgesia, which was accompanied by the increase of spinal ANXA1 and CXCL12/CXCR4 expression. Central injection of Anxa12-26 attenuated behavioral OIH in a dose-dependent manner, facilitated ANXA1 production, and inhibited up-regulation of CXCL12/CXCR4 level and NR2B-containing NMDAR phosphorylation. Moreover, pretreatment with AMD3100 reduced hyperalgesia and NR2B-containing NMDAR phosphorylation. Also, exogenous CXCL12 elicited pain hypersensitivity and NMDAR activation in naïve rats, which was reversed by the supplemental delivery of Anxa12-26. These current findings indicate the participation of spinal CXCL12/CXCR4 and NR2B-containing NMDAR pathway in anti-hyperalgesic action of ANXA1 in OIH.

Attenuation of Remifentanil-Induced Hyperalgesia by Betulinic Acid Associates with Inhibiting Oxidative Stress and Inflammation in Spinal Dorsal Horn.

Remifentanil-induced hyperalgesia (RIH) is known to be associated with oxidative stress and inflammation. Betulinic acid (BA) was reported to reduce visceral pain owing to its anti-oxidative and anti-inflammatory potential. Here, we -explored whether BA can attenuate RIH through inhibiting oxidative stress and inflammation in spinal dorsal horn. Sprague-Dawley rats were randomly divided into 4 groups: Control, Incision, RIH, and RIH pre-treated with BA. After pretreated with BA (25 mg/kg, i.g.) for 7 days, rats were subcutaneously infused with remifentanil (40 µg/kg) for 30 min during right plantar incision surgery to induce RIH. The paw withdrawal mechanical threshold (PWMT), paw withdrawal thermal latency (PWTL), spinal oxidative stress and inflammatory mediators were determined. Intraoperative remifentanil infusion induced postoperative hyperalgesia, as evidenced by the significant decrease in PWMT and PWTL (p < 0.01), and the significant increase in oxidative stress and inflammation evidenced by up-regulations of malondialdehyde, 3-nitrotyrosine, interleukin-1ß and tumour necrosis factor-α (p < 0.01) in spinal dorsal horn and matrix metalloproteinase-9 (MMP-9) activity (p < 0.01) in dorsal root ganglion, as well as a decrease in manganese superoxide -dismutase activity (p < 0.01) compared with control and -incision groups. All these results mentioned above were markedly reversed by pre-treatment with BA (p < 0.01) compared with RIH group. These findings demonstrated that BA can effectively attenuate RIH, which associates with potentially inhibiting oxidative stress and subsequently down-regulating MMP-9-related pro-inflammatory cyokines in spinal dorsal horn.