Betaine Attenuates Hyperhomocysteinemia-Induced Cognitive Impairment by Suppressing Oxidative Stress and Activating the PI3K/AKT/GSK-3β Pathway

High homocysteine levels are a key risk factor for cognitive impairment, a major public health concern in aging societies. Although betaine is known to reduce Hcy levels, its effects on hyperhomocysteinemia (hHcy)-induced cognitive impairment and the underlying mechanisms remain unclear. Here, we established an hHcy-induced cognitive impairment mouse model by feeding mice a high-methionine diet for 8 weeks, followed by betaine supplementation for 14 days. Betaine treatment attenuated hHcy-induced cognitive impairment. This improvement was accompanied by alleviation of neuropathological alterations and enhancement of antioxidant capacity. Notably, betaine suppressed reactive oxygen species (ROS) accumulation, neuronal apoptosis, and Tau hyperphosphorylation at Ser396 and Thr231 in both mouse hippocampus and HT-22 cells. Mechanistically, betaine-induced activation of the PI3K/AKT/GSK-3β pathway was effectively blocked by the PI3K inhibitor LY294002. Notably, treatment with the ROS scavenger N-acetylcysteine (NAC) alone phenocopied this activation, suggesting that ROS functions as an upstream regulator of this signaling cascade. Collectively, our data demonstrate that betaine attenuates hHcy-induced cognitive impairment by suppressing oxidative stress-driven apoptosis and Tau pathology through modulation of the PI3K/AKT/GSK-3β signaling pathway. These findings suggest that betaine may hold promise for further preclinical and clinical studies, although long-term efficacy and safety evaluations remain necessary.