Abstract
Epidemiological evidence suggests that individuals with diabetes mellitus are at greater risk of developing Alzheimer's disease, and controversy overwhelms the usefulness of the widely prescribed insulin-sensitizing drug, metformin, on cognition. Through the scopolamine-induced memory deficit model, we investigated metformin influence on cognitive dysfunction and explored underlying mechanisms. Sixty adult male Wistar rats were randomly assigned into 5 groups (12 rats each) to receive either normal saline, scopolamine 1mg/kg intraperitoneally once daily, scopolamine + oral metformin (100mg/kg/day), scopolamine + oral metformin (300mg/kg/day) or scopolamine + oral rivastigmine (0.75mg/kg/day) for 14days. Cognitive behaviours were tested using Morris water maze and passive avoidance tasks. Biochemically, brain oxidative (malondialdehyde) and inflammatory (TNF-α) markers, nitric oxide, Akt, phospho-Akt, phospho-tau and acetyl cholinesterase activity in hippocampal and cortical tissues were assessed. The lower dose of metformin (100mg/kg) ameliorated scopolamine-induced impaired performance in both Morris water maze and passive avoidance tasks, and was associated with significant reduction of inflammation and to a lesser extent oxidative stress versus rivastigmine. Given the role of total Akt in regulation of abnormal tau accumulation and degradation, our finding that metformin 100 decreased the elevated total Akt while increasing its phosphorylated form explains its beneficial modulatory effect on phosphorylated tau in both tissues, and could further clarify its protection against memory impairment. Metformin, only in the average human antidiabetic dose, offers a protective effect against scopolamine-induced cognitive impairment, while no deleterious effect was observed with the higher dose, which may support a bonus effect of metformin in type 2 diabetic patients.
Published Version
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