Lipocalin-2 in the Anterior Cingulate Cortex Contributes to Remifentanil-Induced Postoperative Hyperalgesia.

Background: Opioids, which are widely used during surgery in perioperative settings, may cause hyperalgesia, especially when the opioid employed is remifentanil. Opioid-induced hyperalgesia may increase the length of a patient's hospital stay and negatively affect enhanced recovery after surgery and the patient's prognosis. Currently, there is no consensus on treatment strategies for remifentanil-induced postoperative hyperalgesia (RIPH).

Objectives: This study aimed to test the hypothesis that upregulation of lipocalin-2 (LCN2) in the anterior cingulate cortex (ACC) contributes to RIPH.

Study design: A controlled animal study.

Setting: A university laboratory.

Methods: The RIPH mouse model was established through the subcutaneous infusion of remifentanil in mice undergoing plantar incision surgery. The von Frey test and the Hargreaves test were used to measure the pain threshold. By combining RNA sequencing, Western blotting, in vivo pharmacology, and the construction of adeno-associated virus vectors that modulated the expression level of LCN2 specifically, the role of LCN2 in the occurrence of RIPH in mice was explored.

Results: Compared to the mice that were subjected to the combination of incisions and saline (inci + saline), mice subjected to incisions and remifentanil (inci + remi) did not experience a significant reduction in the mechanical pain threshold of their ipsilateral hind paws. The mechanical pain threshold of the contralateral hind paws of the inci + remi mice was significantly reduced compared to those of the inci + saline mice. According to transcriptome analysis, LCN2 expression was significantly upregulated in RIPH-model mice. Furthermore, the Western blotting analysis also showed a significant increase in the level of LCN2 in the ipsilateral ACC of RIPH-model mice. An intra-anterior cingulate cortex injection of LCN2 mAb could attenuate hyperalgesia in mice. Knockdown of LCN2 expression in the ACC significantly alleviated mechanical hyperalgesia in mice. Additionally, the overexpression of LCN2 in the ACC could directly induce mechanical hyperalgesia without affecting thermal nociception.

Limitations: Future research needs to explore more potential mechanisms of affecting pain sensitivity through LCN2 upregulation.

Conclusions: Our results demonstrated that the upregulation of LCN2 in the ACC plays a crucial role in the occurrence of RIPH, suggesting that LCN2 potentially be a therapeutic target for alleviating RIPH.