| Summary: | 碩士 === 臺北醫學大學 === 藥理學研究所 === 95 === Accumulating evidence indicates that induction of inducible nitric oxide synthase (iNOS) expression and hence nitric oxide (NO) production has been described to have beneficial antiviral, immunomodulatory, and antitumoral affect. However, induced at the wrong place or at the wrong time, iNOS has detrimental consequences and seems to be involved in the pathophysiology of different human diseases. As such, elevated levels of NO produced within the central nervous system (CNS) are associated with the pathogenesis of neuroinflammatory and neurodegenerative human diseases such as multiple sclerosis, HIV dementia, brain ischemia, trauma, Parkinson''s disease, and Alzheimer''s disease. However, the overactivation of microglia can occur rapidly after the above pathologies of the CNS. In this study, we have observed that oxidized low-density lipoprotein (ox-LDL) and phenytoin affect microglial functions in association with the mechanisms of iNOS expression in microglial cells.
It is well documented that ox-LDL have been shown to play a crucial role in atherosclerosis. The class A scavenger receptor (SR-A) mediates the high affinity binding and internalization of ox-LDL implicated in the development of chronic inflammation. Our results demonstrate that ox-LDL stimulates NO production in microglial cells, and it also stimulates both protein levels and mRNA of iNOS in concentration-dependent manner, indicating that this oxidative components may affect iNOS gene expression. Therefore, we investigated the molecular mechanism of ox-LDL on iNOS expression. Using different pharmacological inhibitors, we found the induction of iNOS by p38 mitogen-activated protein kinase activation. Besides, we even more found that activated p38 in the nucleus induced phosphorylation of activating transcription factor-2 (ATF-2). Taken together, our data clearly demonstrated that ox-LDL-induced microglial cells production of NO and iNOS was mediated mainly by phosphorylation of p38 and ATF-2. On the other hand, we also found that dynamin inhibitor decreased iNOS production in ox-LDL stimulated microglial cells, and fucoidan, SR-A ligand, couldn’t stimulate iNOS production in microglial cells.
Phenytoin is an anticonvulsant drug which can be useful in the treatment of epilepsy clinically. The recent report indicated that sodium channels are important for activation of microglia in encephalomyelitis (EAE) and multiple sclerosis (MS), but the anti-inflammatory mechanisms remain poorly understood. We showed here that phenytoin decreased NO production in LPS-stimulated microglial cells, without affecting cell viability. Besides, we even more found that phenytoin suppressed the expression of iNOS protein induced by LPS in a dose dependent way. Further, we found that phenytoin couldn’t inhibit the LPS-induced IkappaB-alpha degradation suggesting that this drug might not affect LPS-induced activation of NF-kappaB by abrogating the LPS-induced IkappaB-alpha?ndegradation.
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