Remifentanil suppresses increase in interleukin-6 mRNA in the brain by inhibiting cyclic AMP synthesis

Purpose Neuronal inflammation is caused by systemic inflammation and induces cognitive dysfunction. IL-6 plays a crucial role in therapies for neuronal inflammation and cognitive dysfunction. Remifentanil, an ultra-short-acting opioid, controls inflammatory reactions in the periphery, but not in the brain. Therefore, the anti-inflammatory effects of remifentanil in neuronal tissue and the involvement of cAMP in these effects were investigated in the present study. Methods Mice were divided into 4 groups: control, remifentanil, LPS, and LPS + remifentanil. Brain levels of pro-inflammatory cytokine mRNA, and serum levels of corticosterone, catecholamine and IL-6 were measured in the 4 groups. The co-localization of IL-6 and astrocytes in the mouse brain after the LPS injection was validated by immunostaining. LPS and/or remifentanil-induced changes in intracellular cAMP levels in cultured glial cells were measured, and the effects of cAMP on LPS-induced IL-6 mRNA expression levels were evaluated. Results Remifentanil suppressed increase in IL-6 mRNA levels in the mouse brain, and also inhibited the responses of plasma IL-6, corticosterone, and noradrenaline in an inflammatory state. In the hypothalamus, IL-6 was localized in the median eminence, at which GFAP immunoreactivity was specifically detected. In cultured cells, remifentanil suppressed increase in IL-6 mRNA levels and intracellular cAMP levels after the administration of LPS, and this enhanced IL-6 mRNA expression in response to LPS. Conclusion Remifentanil suppressed increase in IL-6 mRNA levels in the brain in an inflammatory state, and this effect may be attributed to its direct action on neuronal cells through the inhibition of intracellular cAMP rather than corticosterone.