Abstract: Objective: To investigate the effects of Moringa leaves on the cognitive dysfunction and apoptosis of hippocampal neurons in diabetic rats induced by streptozotocin (STZ). Methods: Fifty male SD rats were selected, and 10 rats were randomly selected as the control group. The other 40 rats were treated with STZ at the dose of 25 mg/kg by intraperitoneal injection. The 40 diabetic rats were randomly divided into model group, Moringa oleifera low-dose, medium-dose and high-dose group. The rats in Moringa oleifera groups were treated with Moringa oleifera at the doses of 2.0, 4.0 and 8.0 g/kg by gavage, the control group and model group were treated with the same amount of normal saline once a day, for 8 weeks. Morris water maze test was used to evaluate the learning and memory ability of rats. Pathological changes of hippocampal neurons and expressions of Bax, caspase-3 and bcl-2 protein in each group were observed by the sections were stained with HE staining and immunohistochemistry. Enzyme linked immunosorbent assay (ELISA) was used to detect tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6) in rat. Results: compared with the control group, the blood glucose of the model group was increased significantly (P＜0.01), and the blood insulin level was decreased significantly (P＜0.05); compared with the model group, the blood glucose values of Moringa oleifera groups were decreased significantly (P＜0.05, P＜0.01), and the blood insulin levels of middle and high dose Moringa oleifera group were increased significantly (P＜0.05, P＜0.01). There was no significant difference in FBG and INS among the three groups (P＞0.05). In Morris water maze test, compared with the model group, the latency of Moringa oleifera groups was significantly shorter (P＜0.05); the residence time in target quadrant of Moringa oleifera groups with different doses was significantly prolonged (P＜0.05). Compared with the model group, the contents of TNF - α, IL-6 and protein expression in low, medium and high dose groups of Moringa oleifera were decreased significantly (P＜0.05). HE staining and immunohistochemical staining results showed that Moringa oleifera medium dose group was positive, brown yellow, fine granular, compared with the model group. The number of neuronal apoptosis was significantly reduced in the middle dose group (53.21±7.19,P＜0.01); the protein expressions of Bax, caspase-3 and the ratio of Bax/Bcl-2 in hippocampus were significantly decreased in the middle dose group (P＜0.05). Conclusion: The mechanisms of Moringa leaves on the cognitive dysfunction and apoptosis of hippocampal neurons may be related to regulating the protein expressions of Bax, Bcl-2 and Caspase-3, reducing the contents of inflammatory factors TNF-α and IL-6.

Key words: moringa oleifera leaf, diabetes mellitus, cognitive function, inflammatory factors