Effects of Metformin on Metabolic Profile, Cognitive Function, and Neuroinflammation in LDLr⁻/⁻ Mice

Familial hypercholesterolemia (FH), caused by mutations in the low-density lipoprotein receptor (LDLr) gene, has been increasingly associated with brain alterations characteristic of neurodegenerative and mood disorders. Studies with LDLR knockout mice (LDLr ^−/− ) showed that neuroinflammation is a key event in FH-related brain dysfunction. As mTOR inhibition can attenuate these alterations in this model, we hypothesized that metformin, a drug known to modulate mTOR signaling via AMPK activation, could mitigate FH-associated brain changes. To test this, adult LDLr ^−/− mice received daily oral doses of metformin (200 mg/Kg) or vehicle for 30 days. During the final week, behavioral assessments were conducted, including the open-field test (locomotor activity), novel object recognition and object reallocation tasks (memory), and the tail suspension test (depressive-like behavior). Body weight and metabolic parameters, including cholesterol and glucose plasma levels, were analyzed. The mice’s hippocampal astrocyte and microglial density, and gene expression related to neuroinflammation and synaptic plasticity were evaluated. Metformin did not alter total cholesterol levels but significantly improved cognitive performance and reduced depressive-like behavior. Notably, metformin treatment attenuated hippocampal astrogliosis without affecting microglial reactivity. Molecular analysis revealed a downregulation of genes related to neuroinflammation and an upregulation of genes associated with synaptic plasticity after metformin treatment. Accompanying these neuroprotective effects, a trend toward reduced levels of the phosphorylated-to-total mTOR ratio was observed. Overall, metformin improved memory function and astrocyte reactivity in LDLr ^−/− mice, effects that were independent of cholesterol reduction, suggesting its potential as a therapeutic strategy for FH-associated brain dysfunction.