Triptolide inhibits COX-2 expression and PGE2 release by suppressing the activity of NF-κB and JNK in LPS-treated microglia

Activated microglia participate in neuroinflammation which contributes to neuronal damage in neurodegenerative diseases. Inhibition of microglial activation may have potential anti-inflammatory effects. Our laboratory has previously reported that triptolide, a natural biologically active compound extracted from Tripterygium wilfordii, could protect dopaminergic neurons from inflammation-mediated damage. However, the mechanism by which triptolide inhibits inflammation remains unknown. We reported here that inhibition of prostaglandin E-2 (PGE(2)) production could be a potential mechanism of triptolide to suppress inflammation. Triptolide suppressed c-jun NH2-terminal kinase (JNK) phosphorylation, cyclooxygenase 2 (COX-2) expression and PGE(2) production in microglial cultures treated with lipopolysaccharide (LPS). Triptolide also greatly inhibited the transcriptional activity, but not the DNA-binding activity of nuclear factor-kappa B (NF-kappa B) in microglia following LPS stimulation. These results indicate that triptolide might suppress NF-kappa B activity to down-regulate COX-2 expression. The LPS-stimulated transcriptional activity of NF-kappa B was suppressed by inhibition of p38MAPK, but not by that of JNK and extracellular signal-regulated kinase. Furthermore, the LPS-induced PGE(2) production was reduced by inhibiting these kinases. Taken together, these results suggest that triptolide may suppress neuroinflammation via a mechanism that involves inactivation of two parallel signaling pathways: p38-NF-kappa B-COX-2-PGE(2) and JNK-PGE(2).