Dopamine attenuates lipopolysaccharide-induced expression of proinflammatory cytokines by inhibiting the nuclear translocation of NF-κB p65 through the formation of dopamine quinone in microglia.

Many reports have indicated that dopamine has immunomodulatory effects on peripheral immune cells. The purpose of this study was to reveal the immunomodulatory effect of dopamine on the expression of proinflammatory cytokines in microglial cells, which are the immune cells of the central nervous system. In murine microglial cell line BV-2 cells, pretreatment with dopamine for 24 h attenuated the lipopolysaccharide (LPS)-induced expression of proinflammatory cytokines such as tumor-necrosis factor-α, interleukin-1β, and interleukin-6. Neither (5R)-8-chloro-3-methyl-5-phenyl-1,2,4,5-tetrahydro-3-benzazepin-7-ol; hydrochloride (SCH-23390) nor sulpiride, which are dopamine D1-like and D2-like receptor antagonists, respectively, affected the attenuation of LPS-induced expression of cytokines by dopamine. In addition, pretreatment with neither (-)-(6aR,12bR)-4,6,6a,7,8,12b-Hexahydro-7-methylindolo[4,3-a]phenanthridin (CY208-243) nor bromocriptine, dopamine D1-like and D2-like receptor agonists, respectively, was effective in doing so. However, N-acetylcysteine (NAC), which inhibits dopamine oxidation to dopamine quinone, did inhibit this attenuated expression. Dopamine increased the level of quinoproteins, and this increase was inhibited by NAC. Western blot and immunocytochemical analyses revealed that dopamine inhibited LPS-induced nuclear translocation of nuclear factor-kappa B (NF-κB) p65. Dopamine also attenuated the expression of cytokines and the nuclear translocation of NF-κB p65 induced by LPS in mouse microglial cells in primary culture. These results suggest that dopamine attenuated LPS-induced expression of cytokines by inhibiting the nuclear translocation of NF-κB p65 through the formation of dopamine quinone in microglial cells.