Triptolide inhibits amyloid-beta1-42-induced TNF-alpha and IL-1beta production in cultured rat microglia.

Microglia plays an important role in mediating neuroinflammation in Alzheimer's disease (AD). Intervention in microglia activation may exert a neuroprotective effect. In the present study, we reported that oligomeric Abeta1-42 dramatically increased the level of tumor necrosis factor (TNF)-alpha and interleukin (IL)-1beta compared to monomeric and fibrillar Abeta1-42 in rat microglial cultures. Pretreatment of the cultures with triptolide, an anti-inflammatory reagent, alleviated the elevation of TNF-alpha and IL-1beta level induced by oligomeric Abeta1-42. Our results showed that oligomeric Abeta played an important role in mediating neuroinflammation and triptolide was able to suppress the production of pro-inflammatory cytokines from microglia.

Triptolide inhibits COX-2 expression and PGE2 release by suppressing the activity of NF-kappaB 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-kappaB (NF-kappaB) in microglia following LPS stimulation. These results indicate that triptolide might suppress NF-kappaB activity to down-regulate COX-2 expression. The LPS-stimulated transcriptional activity of NF-kappaB 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-kappaB-COX-2-PGE(2) and JNK-PGE(2).

Triptolide upregulates NGF synthesis in rat astrocyte cultures.

Triptolide (T10), an extract from the traditional Chinese herb, Tripterygium wilfordii Hook F (TWHF), has been shown to attenuate the rotational behavior induced by D: -amphetamine and prevent the loss of dopaminergic neurons in the substantia nigra in rat models of Parkinson's disease. To examine if the neuroprotective effect is mediated by its stimulation of production of neurotrophic factors from astrocytes, we investigated the effect of T10 on synthesis and release of nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF) in rat astrocyte cultures. T10 did not affect the synthesis and release of either BDNF or GDNF. However, it significantly increased NGF mRNA expression. It also increased both intracellular NGF and NGF level in culture medium. These results indicate that the neuroprotective effect of T10 might be mediated, at least in part, via a stimulation of the production and release of NGF in astrocytes.