Therapeutic effects of herbal compounds in cerebral ischemia with special reference to suppression of microglia activation implicated in neurodegeneration

Cerebral ischemia affects many especially with the ageing population. The ensuing ischemic reactions include oxidative stress, inflammation, and excitotoxicity among others. In the search for effective therapeutic strategies for cerebral ischemia, activated microglia which are the key player in neuroinflammation are now recognized as a potential therapeutic target. Microglia possess both neurotoxic and neuroprotective roles. They are protective by continuously surveilling the microenvironment, phagocytosing dead cells, secreting trophic factors and sculpting the neuronal connections by removing axons and pruning excess synapses. On the other hand, hyperactivated microglia may impair cerebral oxidative metabolism, and produce excessive proinflammatory mediators that may exacerbate the brain damage. In view of this, suppression of microglial activation has been considered a therapeutic strategy to mitigate microglia-based neuroinflammation in cerebral ischemia. However, balancing the neuroprotective and neurotoxic roles of activated microglia remains a challenging issue. Many traditional Chinese herbal agents have been used in clinic for treatment of cerebral ischemia. Here, we provide an overview of five common Chinese herbs targeting specifically microglia-mediated neuroinflammation in cerebral ischemia. It is hoped that a common parallel may be drawn from their beneficial effects especially in the latter pathological conditions for their better and effective use in the future.