Chronic vitamin D supplementation alleviates cognition impairment via inhibition of oxidative stress regulated by PI3K/AKT/Nrf2 in APP/PS1 transgenic mice.

Oxidative stress plays essential role in the pathogenesis of Alzheimer's disease, and vitamin D (VD) is a nutrient with neuroprotective and antioxidant activities. The present study aimed to confirm the neuroprotective effect and the ameliorative effect of cortical oxidative stress of VD in APP/PS1 transgenic mice. APP/PS1 mice were treated with VD for 20 weeks. After treatment, Morris Water Maze test was used to evaluate cognitive level. Western blotting was used to determine APP, p-tau, tau and PI3K/AKT/Nrf2 pathway-related protein expression levels. Immunohistochemical staining was performed to determine the levels of β amyloid peptide (Aβ) deposition. Enzyme linked immunosorbent assay was used to determine the 25(OH)D levels and oxidative stress status. Our results showed that treatment with VD ameliorated behavioral deficits of APP/PS1 mice. In addition, the administration of VD significantly increased the cortical 25(OH)D levels, while reducing the levels of cortical Aβ deposition and decreasing the expression levels of cortical APP, tau and p-tau in APP/PS1 mice. Moreover, VD protected the cortex against oxidative stress by enhancing the levels of superoxide dismutase, glutathione and total antioxidant capacity, and downregulating the malondialdehyde levels. Furthermore, VD clearly activated the PI3K/AKT/Nrf2 pathway, thereby elevating the expression levels of HO1 and NQO1. We concluded that VD improved cognitive function and cortical Alzheimer-like pathology of APP/PS1 mice, which may be related to the inhibition of oxidative stress via activation the PI3K/AKT/Nrf2 pathway.