Syringic Acid Mitigates Scopolamine-Induced Cognitive Impairment by Regulating PSD-95 and GSK-3β and by Preventing Neurodegeneration in an Alzheimer-Like Rat Model

Abstract

Alzheimer's disease (AD) is a disorder characterized by progressive cognitive impairment. Syringic acid (SA) is a phenolic compound with many beneficial effects, such as antioxidant, anti-inflammatory, anti-diabetic, anticarcinogenic, and neuroprotective. Our study aimed to investigate the effects of SA (50 mg/kg/day) on scopolamine (SCO)-induced AD-like condition in rats. Immunohistochemical evaluation was performed using antibodies to postsynaptic density protein 95 (PSD-95), Glycogen synthase kinase-3 beta (GSK-3 beta), TNF-alpha, and caspase-3. The hippocampus was stained with Hematoxylin-Eosin, and the total number of hippocampal neurons and hippocampal volume were calculated using the stereological method. The Y-maze task behavioral test was performed. SCO decreased PSD-95 expression while increasing GSK-3 beta, TNF-alpha, and caspase-3 expression. SA treatment increased PSD-95 expression while decreasing GSK-3 beta, TNF-alpha, and caspase-3 expression. Compared to the control group, the number of hippocampal neurons was significantly decreased in the Alzheimer's group, but the number of neurons in the SA group was significantly higher than in the Alzheimer's group. Hippocampal volume was lower in the Alzheimer's group, although there was no statistical difference between the groups. SA also improved SCO-induced cognitive impairment. Our study findings suggest that SA may mitigate SCO-induced cognitive impairment in the AD rat model, modulating PSD-95 and GSK-3 beta and decreasing neuroinflammation and apoptosis.