Metformin restores cognitive dysfunction and histopathological deficits in an animal model of sporadic Alzheimer's disease

BACKGROUND: Metformin has been introduced as a neuroprotective agent in recent years. Here we evaluate the therapeutic effects of metformin in sporadic mouse model of Alzheimer's disease (SAD). METHODS: AD was induced by streptozotocin (STZ, 0.5 mg/kg) on days 1 and 3. Metformin (MET, 200 mg/kg per day) was used for two weeks. Novel objective recognition (NOR) and Barnes Maze test were used to test the learning and memory. Nissl staining was used as s histological method for counting the dying neurons in different regions of hippocampus. Immunofluorescence staining against glial fibrillary acidic protein (GFAP), ionized calcium binding adaptor molecule 1 (Iba1) and NeuN were used to visualize reactive astrocytes, microglia and neurons, respectively. RESULTS: In NOR test, the discrimination indices in the STZ group were significantly lower than the control and treatment groups. Goal sector/non-goal sector (GS/NGS) ratio index in Barnes maze was increased in metformin group compared to other groups. The number of dying neurons was increased by SAD and metformin reduced it. GFAP level was increased in CA1, CA3 and cortex of STZ group and reversed following the treatment. Iba1 level was significantly higher in STZ group in CA3 and cortex regions compared to Control and decreased by metformin in CA3 and cortex. Counting NeuN(+) cells demonstrated significant reduction of neurons in DG+CA1 and CA3 after SAD induction. SIGNIFICANCE: Metformin decreased inflammatory cells and reactive astrocytes as well as the dying neurons in the hippocampus region and the cortex in SAD, and improved the cognitive performance.