Exposure-Response Analysis and Mechanism of Ginkgolide B’s Neuroprotective Effect in Acute Cerebral Ischemia/Reperfusion Stage in Rat

Abstract

Ginkgolide B (GKB) is a well-established neuroprotectant for acute ischemia stroke. However, its cerebral exposure and real-time response remain elusive in acute ischemia/reperfusion stage, and it hinders its usage in therapeutic window of ischemia stroke. Therefore, we investigate the exposure-response relationship of GKB (10mg/kg, intravenously (i.v.)) as well as its neuroprotective mechanism in acute ischemia/reperfusion rats. Cerebral and plasma exposure of GKB is comparatively explored in both of normal rats and acute ischemia/reperfusion rats. Correspondingly, neurological function and brain jury indexes were assessed at each time point, and superoxide dismutase (SOD), malondialdehyde (MDA), platelet activator factor (PAF) and thromboxane A2 (TXA2) are indexed as pharmacological response to GKB. Exposure-response relationships are analyzed by using linear regression. Additionally, cerebral expressions of proteins in PAF-regulated pathways are tested at each time point. Results show cerebral and plasma concentrations of GKB are much higher in acute ischemia/reperfusion rats than those in normal rats. Cerebral infarction, neurological function (NF) score, abnormal PAF and excessive MDA are significantly alleviated in 24h after GKB injection, and PAF is reduced in exposure-response manner with significant concentration–response relationship (R2=0.9123). Regarding downstream proteins in intracellular PAF-regulated pathway, GKB progressively inhibits Bax, Caspase-3, p-p65 and p-IKK, while gradually restoring LC3B, p62 and p-mammalian target of rapamycin (mTOR) to the basic level within 24h. Conclusively, GKB exhibits greater cerebral exposure in acute ischemia/reperfusion rats and neuroprotective effect through reducing PAF in exposure-response manner and mediating PAF-regulated intracellular signaling pathways. Our finding highlights clinical implications of GKB in therapeutic time window of ischemic stroke.