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

Abstract

Aims: 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.Materials and methods: 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.Key findings: 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.Significance: 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.