Neuroprotective effect and mechanism of butylphthalide after cerebral ischemia-reperfusion injury in rats

Introduction
To investigate the neuroprotective effect and mechanism of DL-3-n-butylphthalide (NBP) on the brain-derived neurotrophic factor (BDNF)/tyrosine kinase B (TrkB) and its downstream signalling pathway after cerebral ischemia/reperfusion injury (CIRI) in rats.

Material and methods
The middle cerebral artery occlusion/reperfusion (MCAO/R) model was used. Reperfusion was performed 2 h after ischemia, and 20 mg/kg of NBP was intraperitoneally injected. Neurological defect score and pathological changes were performed. Apoptotic cells were detected using in situ end-labelling with TUNEL. The expression of BDNF and TrkB proteins was measured by Western blot and immunohistochemical staining. BDNF mRNA, TrkB mRNA, protein kinase B (AKT) mRNA and caspase-3 mRNA expression were measured using real-time polymerase chain reaction (qPCR).

Results
After 24 h of reperfusion, the neurological defect score and the percentage of apoptotic cells in the ischemia/reperfusion group (I/R group) were higher than those in the ischemia/reperfusion + drug group (I/R + d group). The positive expressions of BDNF and TrkB mRNA and protein in the I/R + d group were obviously higher than those in the I/R group (p < 0.05). After intervention with the TrkB receptor inhibitor (K252a), the expression levels of BDNF and TrkB and AKT mRNA were significantly decreased in the ischemia/reperfusion + drug + TrkB receptor inhibitor group (I/R + d + R group) compared with the I/R + d group, however the caspase-3 mRNA expression level showed the reverse trend. The expressions of BDNF, TrkB and p-Akt proteins in the I/R + d group were remarkably higher than those in the I/R group at each time point, and reached the peak at 24 hours after reperfusion, which were earlier than that in the I/R group.

Conclusions
Butylphthalide represents a neuroprotective effect after CIRI in rats and used within 24 h of early onset contributes to better prognosis. The underlying mechanism may be related to reducing the apoptosis of nerve cells through BDNF/TrkB signalling pathway.