Effect Of Nitidine On Microglia Activation And The Underlying Mechanism

Neuroinflammation is a common result after central nervous system (CNS) injury. Asthe resident immune cell of CNS, microglia plays a pivotal role in neuroinflammation. Inthe normal brain, microglia is present in the resting state, which is characterized by a smallsoma and numerous very thin and highly branched processes. In response to CNS injury,microglia is activated, contracts its processes, transforms from a ramified to an ameboidmorphology and secrets vast numbers of inflammatory mediators, such as cytokines,chemokines and free radicals. Upon activation, microglia can phagocytose and clear thepathogens and cell debris. But over or chronic microglia activation can cause neuronaldeath, and is involved in numerous neurodegeneration conditions. Inhibition of microgliaactivation has been shown to reduce the neuroinflammation and pathological processesafter injury.Nitidine (NTD) is a benzophenanthridine alkaloid extracted from the roots ofZanthoxylum nitidium and is the main effective constitute of this plant. As ananti-inflammatory and analgesic agent, Z. nitidum has been used for more than1000yearsin traditional Chinese medicine. But the role of NTD in CNS has not been reported yet.Based on the LPS induced microglia activation model, we investigated the role ofNTD on regulation of microglia activation by morphology, real-time PCR and western blot.We also investigated the role of NTD in mouse model of cerebral stab wound injury byimmunohistochemistry.The results are as follows:1. Isolation and culture of rat primary microglia. Iba1staining shows that the purity ofprimary microglia is greater than95%.2. NTD inhibits microglia activation. LPS induces dramatic activation of microglia,expressed by morphology change, secretion of proinflammatory cytokines, and increasedability of migration. NTD has a potent inhibition effect on microglia activation.3. All concentrations of NTD applied in research don’t show cytotoxicity. Results ofMTT and LDH show that below1μM, NTD has no cytotoxicity either on N9or primarymicroglia.4. ERK pathway may involve in the regulation of microglia activation by NTD.Investigation of MAPKs demonstrates that NTD can inhibit the phosphorylation of ERKbut not p38and JNK. 5. NTD inhibits microglia activation after cerebral stab wound injury and reducesneuronal apoptosis. After cerebral stab wound injury, mice are administratedintraperitoneally with NTD (2.5mg/kg/day) for3days. Iba1staining shows the number ofmicroglia is remarkably reduced compared to the saline group; and TUNEL assay indicatesthe ratio of apoptotic neuron also declines.