EXPRESS: Curcumin relieves CFA-induced-inflammatory pain by inhibiting the AP-1/c-Jun-CCL2-CCR2 pathway in the spinal dorsal horn

Inflammatory pain is a pervasive clinical issue that severely diminishes individuals’ quality of life. AP-1 (Activating protein-1) is a transcription factor composed of Jun and Fos proteins. Upregulation of AP-1/c-Jun activity is observed in a variety of diseases, particularly in inflammatory conditions. The CCL2 (C-C Motif Chemokine Ligand 2)/CCR2 (C-C Chemokine Receptor 2) axis plays a crucial role in regulating both peripheral and central inflammation. Curcumin, a natural compound derived from the roots of turmeric, possesses anti-inflammatory, antioxidant, and analgesic properties, making it effective for treating various disorders. However, the effects of curcumin on inflammatory pain and its potential mechanisms of action remain unclear. In this study, we utilized a CFA (Complete Freund’s Adjuvant)-induced inflammatory pain model to investigate the effects of curcumin. We found that curcumin effectively reduced CFA-induced mechanical allodynia when administered via intrathecal injection. Behavioral assessments were performed using the Von Frey test. Western blot analysis was performed to detect variations in molecular expression, while immunofluorescence was employed to ascertain cellular localization. Intrathecal injection of the AP-1/c-Jun inhibitor T-5224, along with curcumin, resulted in a reduction in the levels of c-Jun, p-c-Jun, CCL2, and CCR2. Additionally, intrathecal injection of the CCR2 antagonist RS504393 also reduced the expression of CCL2 and CCR2. In summary, curcumin plays a significant role in analgesia within the CFA-induced inflammatory pain model. CCL2/CCR2 acts as a downstream mediator of AP - 1/c - Jun. Curcumin can suppress the expression of AP - 1/c - Jun, thereby inhibiting the expression of CCL2 and CCR2 in the spinal dorsal horn and contributing to the treatment of inflammatory pain.