Hippocampal Klotho expression is associated with the neuroprotective effects of metformin against ICV-STZ-induced...

Alzheimer's disease (AD) is characterized by progressive cognitive decline, amyloid-β (Aβ) accumulation, oxidative stress, and neuroinflammation. Increasing evidence links metabolic dysfunction to AD, suggesting that antidiabetic drugs such as metformin may exert neuroprotective effects. This study investigated the effects of long-term metformin pretreatment on cognitive function, hippocampal pathology, and neuroprotective gene expression in an intracerebroventricular streptozotocin (ICV-STZ) rat model of AD. Adult male Sprague-Dawley rats were assigned to Sham, STZ, Metformin, and STZ + Metformin groups. Metformin (2 g/L in drinking water) was administered for 12 weeks before ICV-STZ injection. Spatial learning and memory were assessed using the Morris water maze. Hippocampal pathology was evaluated by H&E, Nissl, and Congo red staining, and gene expression was analyzed by quantitative PCR. ICV-STZ induced cognitive impairment, hippocampal Aβ deposition, neuronal loss, and increased expression of pro-inflammatory and oxidative stress markers. Metformin pretreatment significantly improved spatial learning and memory, reduced amyloid burden, and preserved neuronal integrity in the CA1 and CA3 regions. Metformin increased hippocampal Klotho mRNA expression, enhanced antioxidant defenses (Nrf2 and HO-1), suppressed TNF-α, IL-1β, and iNOS expression, and increased IL-10 levels. Although BDNF mRNA expression showed an upward trend, the change was not statistically significant. No significant changes in blood glucose levels were observed. In conclusion, long-term metformin pretreatment attenuated STZ-induced AD-like pathology and cognitive deficits. Its neuroprotective effects were associated with increased hippocampal Klotho expression and reduced oxidative stress and neuroinflammation, supporting further investigation of metformin and the Klotho pathway as potential preventive strategies for AD.