Objective To observe protective effect of Lycium barbarum polysaccharide (LBP) on hippocampal neuron injury induced by radiation in vivo and in vitro and to explore the associations of oxidative stress and PI3K/Akt/mTOR signaling pathway with the effect in rats and rat embryonic cells.

Methods For in vivo experiment, Sprague-Dawley (SD) rats were divided into three groups (16 in each group): model group (ModA) with a single electron beam irradiation on brain at the dosage of 20 Gy and saline gavage, LBP group (LBPA) with intragastric administration of 50 mg/kg LBP two weeks before the irradiation, and control group (ConA) without irradiation but with saline gavage. Thirty days after the treatments, water maze test was used to test cognitive function of the rats; Nissl-stained hippocampal tissues were observed; TdT-mediated dUTP-biotin nick end-labeling (TUNEL) method was been employed to detect apoptosis of hippocampal neurons; malondialdehyde (MDA), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) in hippocampal tissue homogenate were detected. For in vitro experiments, hippocampal neurons of primary fetal SD rats were cultured and also divided into three groups: model group (ModB) with single 30 Gy X-ray irradiation LBP group (LBPB) with the irradiation and LBP administration in culture fluid one hour before the irradiation at the concentration of 50 μg/ml, and control group(ConB) without the irradiation and LBP treatment. Cell activity was determined with 3-4,5-dimethylthiazol-2-yl-2,5-diphenyl tetrazolium bromide (MTT) assay; cell apoptosis was detected with annexin V-fluorescein/propidium iodide (FITC/PI) flow cytometry; and protein expressions of phosphatidylinositol-3-kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin (mTOR), B-cell lymphoma/leukemia 2 (bcl-2), Bcl-2 associated X protein (Bax) and caspase-3 were detected with Western blot.

Results Compared with those of the ModA rats, the escape latency period and space exploration time of LBPA rats were significantly shortened; the morphology of damaged hippocampal neurons was significantly improved; and the apoptosis rate was significantly reduced. The LBPA rats had significantly lower MDA content and significantly higher SOD and GSH-Px activity than the ModA rats (P < 0.01 for all). In comparison with the ModB cells, LBPB cells showed increased survival rate, decreased apoptosis rate, significantly increased expression of PI3K, pAkt, mTOR and bcl-2, and decreased expression of Bax and caspase-3 (all P < 0.01).

Conclusion LBP can inhibit radiation-induced apoptosis of hippocampal neurons and the neuroprotective effect may be related to regulations of PI3K/Akt/mTOR signaling pathway and oxidative stress.