Nrf2 mediates the antinociceptive activity of dexmedetomidine in an acute inflammatory visceral pain rat model by activating the NF-κB sensor

Dexmedetomidine (DEX) is a highly selective alpha 2 adrenoceptor agonist. In this study, we evaluated the antalgic effect of DEX on acetic acid-induced acute inflammatory visceral pain (AIVP) in rats. Additionally, we evaluated the role of Nrf2 signalling in antinociception. We administered acetic acid to male Sprague Dawley rats that were treated with DEX or saline. Twenty rats were randomly classified into the following groups: normal, model, vehicle, or DEX group. Both q-RT PCR and enzyme-linked immunosorbent assay data suggested that interleukin 1 beta (IL-1 beta), tumour necrosis factor alpha, and IL-6 were upregulated in the spinal cord. Western blotting and q-RT PCR analyses were performed to detect the protein and mRNA expression levels of Nrf2, Keap1, and HO-1 in the spinal cord. The DEX group exhibited a significant downregulation in Nrf2/Keap1/HO-1 signal activation compared with the model group. Furthermore, we used the Nrf2(-/-) knockout AIVP rat model to determine the role of Nrf2 in the antinociceptive effect of DEX. We observed that the Nrf2 knockout blocked the Keap1/Nrf2/HO-1 signal transduction and partially abated the antinociceptive and the anti-inflammatory effects of DEX. Moreover, our data also indicated that DEX treatment decreased the activation and expression of nuclear factor (NF)-kappa B. However, Nrf2 silencing restored the expression of NF-kappa B and its phosphorylated form to physiological levels. In summary, our results suggested that Nrf2 signalling plays an important role in the antinociceptive effect of DEX in the AIVP rat model and that Nrf2 exerts its function by enhancing the activation of the NF-kappa B sensor. Significance of the study Currently, using the behavioural parameters is not adequate for the diagnosis of AIVP, and there are no studies that have investigated the role and the mechanism of DEX in ameliorating visceral pain. In this study, we demonstrated that acetic acid stimulation in rats induces AIVP. Additionally, the administration of DEX inhibited the acute inflammation response and decreased the visceromotor reaction (behavioural) to algesia. Further, DEX inhibited the Keap1/Nrf2 pathway, which was activated by acetic acid treatment. We suggest that suppressing the inflammatory response could partially regulate the antinociceptive effect of DEX through Nrf2-mediated NF-kappa B activation associated with AIVP.