Ginsenoside Rg1 attenuates lipopolysaccharide-induced inflammatory responses via the phospholipase C-γ1 signaling pathway in murine BV-2 microglial cells.

ABSTRACT

BACKGROUND AND PURPOSE: Microglial activation plays an important role in neurodegenerative diseases by producing an array of proinflammatory enzymes and cytokines. Ginsenoside Rg1 (Rg1), a well-known Chinese herbal medicine, has been well recognized for its anti-inflammatory effect. This study sought to determine the anti-inflammatory effects of Rg1 and its underlying mechanisms in lipopolysaccharide (LPS)-stimulated murine BV-2 microglial cells. EXPERIMENTAL APPROACH: Murine BV-2 microglial cells were treated with Rg1 (10, 20, and 40 µM) and/or LPS (1 µg·ml(-1)). The mRNA and protein levels of proinflammatory proteins and cytokines were analysed by RT-PCR assay and double immunofluorescence labeling, respectively. Phosphorylation levels of mitogen-activated protein kinases (MAPKs) cascades, inhibitor κB-α (IκB-α) and cyclic AMP- responsive element (CRE)-binding protein (CREB) were measured by western blot. U73122 (5 µM), a specific phospholipase C (PLC) inhibitor, was used to determine if PLC signaling pathway might be involved in Rg1's action on activated BV-2 cells. KEY RESULTS: Pretreatment with Rg1 significantly attenuated the LPS-induced expression of inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), tumor necrosis factor-α (TNF-α), interleukin-1ß (IL-1ß) and nuclear factor-κB (NF-κB) in BV-2 cells. U73122 blocked the effects of Rg1 on LPS-induced microglial activation. In addition, PLC-γ1 inhibition partially abolished the inhibitory effect of Rg1 on the phosphorylation of IκB-α, CREB, extracellular signal-regulated kinase 1/2 (ERK1/2), c-Jun N-terminal protein kinase (JNK), and p38 mitogen-activated protein kinase (p38 MAPK). CONCLUSION AND IMPLICATIONS This investigation demonstrates that Rg1 significantly attenuates overactivation of microglial cells by repressing expression levels of neurotoxic proinflammatory mediators and cytokines via activation of PLC-γ1 signaling pathway.