A great deal of attention has been paid to neuroprotective therapies for cerebral ischemic stroke. Our two recent clinical trials showed that ginsenoside Rd (Rd), a kind of monomeric compound extracted from Chinese herbs, Panax ginseng and Panax notoginseng, was safe and efficacious for the treatment of ischemic stroke. In this study, we conducted a pooled analysis of the data from 199 patients with acute ischemic stroke in the first trial and 390 in the second to reanalyze the efficacy and safety of Rd. Moreover, animal stroke models were carried out to explore the possible molecular mechanisms underlying Rd neuroprotection. The pooled analysis showed that compared with placebo group, Rd could improve patients' disability as assessed by modified Rankin Scale (mRS) score on day 90 post-stroke and reduce neurologic deficits on day 15 or day 90 post-stroke as assessed by NIH Stroke Scale (NIHSS) and Barthel Index (BI) scores. For neuroprotective mechanisms, administration of Rd 4 h after stroke could inhibit ischemia-induced microglial activation, decrease the expression levels of various proinflammatory cytokines, and suppress nuclear factor of kappa light polypeptide gene enhancer in B cells inhibitor, alpha (IκBα) phosphorylation and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) nuclear translocation. An in vitro proteasome activity assay revealed a significant inhibitory effect of Rd on proteasome activity in microglia. Interestingly, Rd was showed to have less side effects than glucocorticoid. Therefore, our study demonstrated that Rd could safely improve the outcome of patients with ischemic stroke, and this therapeutic effect may result from its capability of suppressing microglial proteasome activity and sequential inflammation.

Phosphorylated tau was found to be regulated after cerebral ischemia and linked to high risk for the development of post-stroke dementia. Our previous study showed that ginsenoside Rd (Rd), one of the main active ingredients in Panax ginseng, decreased tau phosphorylation in Alzheimer model. As an extending study, here we investigated whether Rd could reduce tau phosphorylation and sequential cognition impairment after ischemic stroke. Sprague-Dawley rats were subjected to focal cerebral ischemia. The tau phosphorylation of rat brains were analyzed following ischemia by Western blot and animal cognitive functions were examined by Morris water maze and Novel object recognition task. Ischemic insults increased the levels of phosphorylated tau protein at Ser199/202 and PHF-1 sites and caused animal memory deficits. Rd treatment attenuated ischemia-induced enhancement of tau phosphorylation and ameliorated behavior impairment. Furthermore, we revealed that Rd inhibited the activity of Glycogen synthase kinase-3β (GSK-3β), the most important kinase involving tau phosphorylation, but enhanced the activity of protein kinase B (PKB/AKT), a key kinase suppressing GSK-3β activity. Moreover, we found that LY294002, an antagonist for phosphatidylinositol 3-kinase (PI3K)/AKT signaling pathway, abolished the inhibitory effect of Rd on GSK-3β activity and tau phosphorylation. Taken together, our findings provide the first evidence that Rd may reduce cerebral ischemia-induced tau phosphorylation via the PI3K/AKT/GSK-3β pathway.

Ginsenoside Rd (Rd), one of the main active ingredients in Panax ginseng, has been showed to protect against ischemic cerebral damage both in vitro and in vivo. However, the underlying mechanism of Rd is largely unknown. Excessive extracellular glutamate causes excitatory toxicity, leading to cell death, and neurodegenerative processes after brain ischemia. The clearance of extracellular glutamate by astrocytic glutamate transporter GLT-1 is essential for neuronal survival after stroke. Here we investigated the effects of Rd on the levels of extracellular glutamate and the expression of GLT-1 in vivo and in vitro. After rat middle cerebral artery occlusion, Rd significantly increased the mRNA and protein expression levels of GLT-1, and reduced the burst of glutamate as revealed by microdialysis. Consistently, specific glutamate uptake by cultured astrocytes was elevated after Rd exposure. Furthermore, we showed that Rd increased the levels of phosphorylated protein kinase B (PKB/Akt) and phospho-ERK1/2 (p-ERK1/2) in astrocyte culture after oxygen–glucose deprivation. Moreover, the effect of Rd on GLT-1 expression and glutamate uptake can be abolished by PI3K/AKT agonist LY294002 or ERK1/2 inhibitor PD98059. Taken together, our findings provide the first evidence that Rd can promote glutamate clearance by up-regulating GLT-1 expression through PI3K/AKT and ERK1/2 pathways.

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