Neuroprotection against cerebral ischemia/reperfusion by dietary phytochemical extracts from Tibetan turnip (Brassica rapa L.)

Ethnopharmacological relevance: The Tibetan turnip (Brassica rapa L.) has a wide array of medicine properties including heat-clearing, detoxifying and anti-hypoxia as listed in the famous centuries-old Tibetan medicine classic "The Four Medical Tantras". Recent evidence-based medicine also indicates the anti-hypoxic effect of turnips, suggesting a potential link to neuroprotective effect on ischemic stroke. This thereby enables turnips to serve as a novel nontoxic agent in related treatment.

Aim of the study: This study aimed to investigate the neuroprotective effect and detailed mechanism of turnip water extraction phase (TWEP) on cerebral ischemia/reperfusion in vivo and in vitro.

Materials and methods: The experimental modelling of cerebral ischemia includes oxygen-glucose deprivation/reoxygenation (OGD/R) to in vitro HT-22 cells and transient middle cerebral artery occlusion/reperfusion (MCAO). Efficacy of TWEP was determined by HT-22 cell viability and by the release of lactate dehydrogenase (LDH) and reactive oxygen species (ROS). The underlying mechanism by which TWEP rescues OGD/R cells was characterized by the expression of PI3K, Akt and mTOR with LY294002 (PI3K inhibitor) used to further validate TWEP's role in the pathway. Long-term effect of TWEP on infarct volume was evaluated by microtubule-associated protein 2 (MAP2) immunofluorescence 28 days after MCAO, and on neurofunctional outcomes determined by rotarod, grid walking, and cylinder tests in the meantime.

Results: Suitable concentrations of TWEP are able to restore OGD/R-induced extensively increased level of ROS and LDH, impaired mitochondrial expression and thereby cell viability. Phosphorylation of PI3K, Akt, mTOR, weakened by OGD/R, can be restored with TWEP treatment, whereas LY294002 can block this improvement. In vivo experiment further demonstrated that TWEP can reduce cerebral infarct volume and ameliorate behavioral deficits of MCAO/R mice dose-dependently.

Conclusions: TWEP inhibits the apoptosis of OGD/R-injured HT-22 cells by activating the PI3K/Akt/mTOR pathway. Based on the results above, turnip extract has a protective effect on focal cerebral ischemic injury.

Keywords: Brassica rapa L.; Cerebral ischemia/reperfusion; Neuroprotection; PI3K/AkT/mTOR.