Bernd L. Fiebich

Inhibition of neuroinflammation in LPS-activated microglia by cryptolepine

Cryptolepine, an indoloquinoline alkaloid in Cryptolepis sanguinolenta, has anti-inflammatory property. In this study, we aimed to evaluate the effects of cryptolepine on lipopolysaccharide (LPS)- induced neuroinflammation in rat microglia and its potential mechanisms. Microglial activation was induced by stimulation with LPS, and the effects of cryptolepine pretreatment on microglial activation and production of proinflammatory mediators, PGE2/COX-2, microsomal prostaglandin E2 synthase and nitric oxide/iNOS were investigated. We further elucidated the role of Nuclear Factor-kappa B (NF-κB) and the mitogen-activated protein kinases in the antiinflammatory actions of cryptolepine in LPS-stimulated microglia. Our results showed that cryptolepine significantly inhibited LPS-induced production of tumour necrosis factor-alpha (TNFα), interleukin-6 (IL-6), interleukin-1beta (IL-1β), nitric oxide, and PGE2. Protein and mRNA levels of COX-2 and iNOS were also attenuated by cryptolepine. Further experiments on intracellular signalling mechanisms show that IκB-independent inhibition of NF-κB nuclear translocation contributes to the anti-neuroinflammatory actions of cryptolepine. Results also show that cryptolepine inhibited LPS-induced p38 and MAPKAPK2 phosphorylation in the microglia. Cell viability experiments revealed that cryptolepine (2.5 and 5u2009μM) did not produce cytotoxicity in microglia. Taken together, our results suggest that cryptolepine inhibits LPS-induced microglial inflammation by partial targeting of NF-κB signalling and attenuation of p38/MAPKAPK2.

The anti-inflammatory effects of the 5-HT3 receptor antagonist tropisetron are mediated by the inhibition of p38 MAPK activation in primary human monocytes

BACKGROUNDnThere is evidence from human and animal research that 5-hydroxytryptamine (5-HT) 3 receptor antagonists, particularly tropisetron, exert analgesic and anti-inflammatory activity. We have demonstrated that tropisetron inhibited lipopolysaccharide (LPS)-stimulated tumor necrosis factor (TNF)alpha and interleukin-(IL-)1beta release in primary human monocytes. The underlying mechanisms of these effects have not been investigated in detail so far.nnnMETHODSnThe molecular mechanisms of the anti-inflammatory effects of tropisetron were investigated in human primary monocytes in vitro by studying IL-1beta and TNFalpha mRNA levels by PCR and reporter gene assay and by elucidating the phosphorylation of p38 mitogen activated kinase (MAPK) by Western blot.nnnRESULTSnThe steady state levels of IL-1beta and TNFalpha mRNA in LPS-activated human peripheral monocytes and the transcriptional activity of the TNFalpha promoter were not inhibited by tropisetron, suggesting that the inhibitory activity of this 5-HT₃ receptor antagonist takes place at the post-transcriptional level. Additionally, we found that tropisetron prevents the phosphorylation and thus activation of the p38 MAPK, which is involved in post-transcriptional regulation of various cytokines.nnnCONCLUSIONnOur data indicate that the anti-inflammatory effects of the 5-HT₃ receptor antagonist tropisetron, as shown in vivo, are possibly mediated by a selective inhibition of pro-inflammatory cytokines at the post-transcriptional level. 5-HT₃ receptor antagonists are therefore a new and promising therapeutic option. New and more selective--in respect to the 5-HT₃ subtypes--5-HT₃R antagonists might be a future perspective in the pharmacological treatment of inflammatory diseases.

Salicin from Willow Bark can Modulate Neurite Outgrowth in Human Neuroblastoma SH‐SY5Y Cells

Salicin from willow bark has been used throughout centuries in China and Europe for the treatment of pain, headache, and inflammatory conditions. Recently, it could be demonstrated that salicin binds and activates the bitter taste receptor TAS2R16. Studies on rodent tissues showed the general expression of bitter taste receptors (TAS2Rs) in rodent brain. Here, we demonstrate the expression of hTAS2R16 in human neuronal tissues and the neuroblastoma cell line SH‐SY5Y. The functionality was analyzed in the neuroblastoma cell line SH‐SY5Y after stimulation with salicin, a known TAS2R16 agonist. In this setting salicin induced in SH‐SY5Y cells phosphorylation of ERK and CREB, the key transcription factor of neuronal differentiation. PD98059, an inhibitor of the ERK pathway, as well as probenecid, a TAS2R16 antagonist, inhibited receptor phosphorylation as well as neurite outgrowth. These data show that salicin might modulate neurite outgrowth by bitter taste receptor activation. Copyright

Traditional African Medicine as a source of biologically active substances inhibiting neuroinflammation

Traditional Africa Medicine (TAM) refers to indigenous forms of healing that are practiced all over Africa. One of the most important forms of TAM is the use of herbal extracts for the prevention and treatment of diseases. Neuroinflammation has been shown to be a critical aspect of neurodegenerative disorders, including Alzheimers disease. Here we show that extracts and bioactive compounds obtained from African plants are able to inhibit neuroinflammatory processes. Our research has shown that cryptolepine, an alkaloid of the West African shrub, Cryptolepis sanguinolenta (Lindl.) Schltr (Apocynaceae) inhibits neuroinflammation in lipopolysaccharide-(LPS)-activated microglia. This alkaloid has been shown to inhibit inflammatory mediator release from activated microglia through mechanisms involving NF-kB and p38 MAPK signalling. Cryptolepine also produced anti-neuroinflammatory actions in IL-1β-stimulated SK-N-SH neuronal cells. Other African plants which have been shown to exhibit varying degrees of inhibition of neuroinflammation are Anacardium occidentale, Bridelia ferruginea, Picralima nitida and Capsicum extract [1], [2]. The results presented in this talk provide a molecular basis for the potential of these African plants in neuroinflammation

5-HT3 receptor expression in primary human monocytes

There is evidence that 5-hydroxytryptamine-3 (5-HT3) receptor antagonists may be useful for treatment of inflammatory disorders. Studies from human and animal research showed that 5-HT3 receptor antagonists, particularly tropisetron, exert analgesic and anti-inflammatory activity. We have demonstrated that tropisetron inhibited the release of inflammatory mediators such as tumor necrosis factor (TNF) in primary human monocytes. So far, the underlying mechanisms of these effects have not been investigated in detail. This is especially true for the role of the 5-HT3 receptor subtypes A,B,C,D,E in inflammatory events. Here, we investigated the effects of tropisetron and lipopolysaccharide (LPS) on the expression of 5HT3 receptor A,B,C,D,E mRNA levels by real time PCR and FACS analysis. Our data indicate that the different 5-HT3 receptor subtypes are modulated at its transcriptional and surface expression level by inflammatory conditions and 5-HT3 antagonists such as tropisetron in primary human monocytes. 5-HT3 receptor antagonists are therefore a new and promising therapeutic option. New and more selective – in respect to the 5-HT3 subtypes – 5-HT3R antagonists might be a future perspective in the pharmacological treatment of inflammatory diseases such as rheumatoid arthritis.