Neuroprotective effect of peptides extracted from walnut (Juglans Sigilata Dode) proteins on Aβ25-35-induced memory impairment in mice.

Alzheimer's disease (AD) is one of the major neurodegenerative disorders of the elderly, which is characterized by the accumulation and deposition of amyloid-beta (Aβ) peptide in human brains. Oxidative stress and neuroinflammation induced by Aβ in brain are increasingly considered to be responsible for the pathogenesis of AD. The present study aimed to determine the protective effects of walnut peptides against the neurotoxicity induced by Aβ25-35 in vivo. Briefly, the AD model was induced by injecting Aβ25-35 into bilateral hippocampi of mice. The animals were treated with distilled water or walnut peptides (200, 400 and 800 mg/kg, p.o.) for five consecutive weeks. Spatial learning and memory abilities of mice were investigated by Morris water maze test and step-down avoidance test. To further explore the underlying mechanisms of the neuroprotectivity of walnut peptides, the activities of superoxide dismutase (SOD), glutathione (GSH), acetylcholine esterase (AChE), and the content of malondialdehyde (MDA) as well as the level of nitric oxide (NO) in the hippocampus of mice were measured by spectrophotometric method. In addition, the levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), tumor necrosis factor-α (TNF-α), interleukin 1β (IL-1β) and IL-6 in the samples were determined using ELISA. The hippocampal expressions of inducible nitric oxide synthase (iNOS) and nuclear factor κB (NF-κB) were evaluated by Western blot analysis. The results showed that walnut peptides supplementation effectively ameliorated the cognitive deficits and memory impairment of mice. Meanwhile, our study also revealed effective restoration of levels of antioxidant enzymes as well as inflammatory mediators with supplementation of walnut peptides (400 or 800 mg/kg). All the above findings suggested that walnut peptides may have a protective effect on AD by reducing inflammatory responses and modulating antioxidant system.