Herbal Compounds with Special Reference to Gastrodin as Potential Therapeutic Agents for Microglia Mediated Neuroinflammation

Background: Activated microglia play a pivotal role neurodegenerative diseases by producing a variety of proinflammatory mediators including tumor necrosis factor-alpha (TNF-α), interleukin- 1beta (IL-1β) and nitric oxide (NO) that are toxic to neurons and oligodendrocytes. Methods: In view of the above, suppression of microglia mediated neuroinflammation is deemed a therapeutic strategy for neurodegenerative diseases. Several potential Chinese herbal extracts have been reported to exert neuroprotective effects against neurodegenerative diseases targeting specifically at the activated microglia. In this connection, the phenolic glucoside gastrodin, a main constituent of the Chinese herbal medicine Gastrodia rhizoma, produced widely in the local community exhibits potential neuroprotective effects through suppression of neurotoxic proinflammatory mediators. Results: Here, we first review the roles of activated microglia in different brain diseases. The effects of gastrodin on activated microglia are then considered. We have identified gastrodin as a putative therapeutic agent as it has been found to suppress microglial activation thus ameliorating neuroinflammation. More importantly, gastrodin downregulates the expression of renin angiotensin system (RAS) and production of proinflammatory mediators. Remarkably, gastrodin promotes Sirtuin 3 (Sirt3) up-regulation and nicotinamide adenine dinucleotide phosphate oxidase-2 (NOX-2) down-regulation after ischemichypoxia in activated microglia mediated by AT1 or AT2 receptors which are angiotensin II receptors subtypes, indicating a possible molecular link between RAS and Sirt3 survival genes. Conclusion: This review summarizes the beneficial effects of gastrodin acting on activated microglia along with other herbal compounds. Its efficacy in neuroprotection is consistent with some common herbal products in China.