Differential effects of ginsenosides on NO and TNF-α production by LPS-activated N9 microglia

Ginsenosides, the main active components of ginseng, have been reported to exert neuroprotective effects in the central nervous system. In this report, the effects of ginsenoside-Rd and -Rb2, two protopanaxadiols, and ginsenoside-Rg1 and -Re, two protopanaxatriols, on the production of nitric oxide (NO) and TNF-alpha (TNF-α) by lipopolysaccharide (LPS)-activated N9 microglial cells were studied. All ginsenosides studied potently suppressed TNF-α production in LPS-activated N9 cells. Ginsenoside-Rg1 and -Re, but not ginsenoside-Rb2 and -Rd, inhibited the production of NO in LPS-activated N9 cells. Ginsenosides inhibited the phosphorylation of c-Jun NH2-terminal kinase (JNK), c-Jun and extracellular signal-regulated kinase (ERK), The findings herein show that the inhibition of LPS-induced ERK1/2 and JNK activation may be a contributing factor to the main mechanisms by which ginsenosides inhibits RAW264.7. To clarify the mechanistic basis for its ability to inhibit TNF-α and NO induction, the effect of ginsenosides on transcription factor NF-κB protein level was also examined. These activities were associated with the down-regulation of inhibitor κB (IκB). These findings suggest that the inhibition of LPS-induced NO formation and TNF-α production in microglia by ginsenosides is due to its inhibition of NF-κB, which may be the mechanistic basis for the anti-inflammatory effects of ginsenosides. The significant suppressive effects of ginsenosides on proinflammatory responses of microglia implicate their therapeutic potential in neurodegenerative diseases accompanied by microglial activation.