Dopamine decreases LPS-induced expression of proinflammatory cytokines in microglial cells through the formation of dopamine quinone in the mouse striatum.

We previously reported that pretreatment with dopamine decreased lipopolysaccharide (LPS)-induced expression of proinflammatory cytokines through the formation of dopamine quinone in cultured microglial cells, and that loss of dopaminergic neurons induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) enhanced LPS-induced mRNA expression of proinflammatory cytokines in the mouse striatum. In this study, we examined the effect of L-dopa/carbidopa on the enhancement of LPS-induced mRNA expressions of proinflammatory cytokines by MPTP in the mouse striatum. The levels of cytokine mRNA and quinoprotein, an indicator of dopamine quinone formation, in the striatum were examined by real-time RT-PCR and NBT/glycinate assay, respectively. Co-administration of L-dopa (50 mg/kg) and carbidopa (5 mg/kg), once daily for 5 days, significantly attenuated the enhancement of LPS-induced increase in mRNA levels of TNF-α, IL-1β, and IL-6 by MPTP in the striatum. The decrease of quinoprotein level in the striatum by MPTP was also attenuated by the co-administration of L-dopa and carbidopa. These results suggest that dopamine decreases LPS-induced expression of proinflammatory cytokines in microglial cells through the formation of dopamine quinone in the mouse striatum.