Puerarin suppresses production of nitric oxide and inducible nitric oxide synthase in lipopolysaccharide- induced N9 microglial cells through regulating MAPK

Microglial cells play a critical role in mediating central nervous system inflammatory processes. Activated microglial cells induced by proinflammatory factor, such as lipopolysaccharide (LPS), release many kinds of neurotoxic cytokines including reactive oxygen species (ROS) which contributes to the pathogenesis of neurodegenerative diseases. Puerarin, extracted from kudzu root, possesses the characteristic of neuroprotection, antioxidation and anticancer. In the present study, we observed that LPS induced over-production of nitric oxide (NO) and increased the level of intracellular ROS in N9 microglial cells, but it was inhibited by puerarin. Furthermore, treatment with puerarin on N9 cells suppressed the over-expression of inducible nitric oxide synthase (iNOS) induced by LPS which is implicated in intracellular O-linked β-N-acetylglucosamine (O-GlcNAc) level, phosphorylation of mitogen-activated protein kinase (MAPK) and nuclear factor κB (NF-κB) signaling pathway. We also observed that the enhanced phosphorylation of p38, JNK and ERK1/2 in N9 cells induced by LPS were inhibited by puerarin, otherwise the down-regulation of O-GlcNAcylation level of protein in N9 cell induced by LPS was up-regulated by pretreatment with puerarin. These results indicate that puerarin effectively inhibits microglia activation induced by LPS through inhibiting expression of iNOS, production of NO and ROS which was mediated via regulating O-GlcNAcylation, phosphorylation of MAPK and NF-κB translocation.