Metformin protects against insulin resistance-related dementia risk involving restored microglial homeostasis

The rising prevalence of type 2 diabetes (T2D), obesity, and metabolic syndrome highlights the need for therapeutic strategies addressing both metabolic and neurological aspects of these conditions. This study evaluates the potential of metformin, a widely prescribed antidiabetic drug, to mitigate hippocampal changes induced by a moderate high-fat diet (HFD) and explores its mechanisms beyond glycemic regulation, including modulation of microglial autophagy, mitochondrial turnover, and neuroinflammation.

We analyzed data from diabetic patients enrolled in the NACC study, a retrospective observational study, to assess cognitive outcomes associated with metformin use. Additionally, we examined the effects of metformin in HFD-treated mice, evaluating hippocampal insulin resistance, synaptic marker and microglial status. We also employed BV2 microglial cells exposed to palmitate as a lipotoxic stimulus to assess the potential of metformin in modulating microglial autophagy, mitochondrial status and inflammatory response.

In diabetic patients, metformin use is associated with improved memory and executive function, independent of cardiovascular risk factor control. In HFD-treated mice, metformin reduced hippocampal insulin resistance, increased synaptophysin levels, and reversed microglial activation and autophagy impairment. In BV2 microglial cells, metformin reduced IL-1β and TNFα expression, restored autophagic flux, and regulated mitochondrial turnover, leading to decreased mitochondrial ROS production.

Our findings suggest that metformin exerts therapeutic effects beyond glycemic control in the context of T2D. By mitigating neuroinflammation and modulating microglial autophagy, metformin emerges as a promising therapeutic agent for cognitive decline associated with diabetes and potentially other neurological disorders.