Glycyrrhizic Acid Ameliorates Cognitive Impairment in a Rat Model of Vascular Dementia Associated with Oxidative Damage and Inhibition of Voltage-Gated Sodium Channels

Vascular dementia (VD) is the second most common cause of cognitive impairment in the elderly population. Our study aims to investigate the neuroprotective effects of glycyrrhizic acid (GA), a major active constituent of Glycyrrhiza glabra root, in a VD rat model induced by permanent occlusion of the bilateral common carotid arteries. Spatial cognitive function was examined by the Morris water maze test and synaptic plasticity was explored by assessing long-term potentiation. The results showed that GA (20 mg/kg for 5 days) significantly improved the performance of learning and memory of VD rats in the Morris water maze test and attenuated induction of long-term potentiation. Histopathological studies showed that GA significantly attenuated cell damage in VD rats. Malondialdehyde levels and superoxide dismutase activity were analyzed in the hippocampus and cortex to investigate anti-oxidant status. The results showed that GA decreased the level of lipid peroxidation and increased the activity of superoxide dismutase in VD rats. Lastly, whole-cell patch-clamp analysis was used to examine the effect of GA on voltage-gated sodium channels (VGSCs) in hippocampal CA1 pyramidal neurons. GA (10, 20 and 50 μM) inhibited the current amplitude of the VGSCs. These results suggest that the neuroprotective effects of GA in VD rats relate to the reduction of oxidative stress and inhibition of VGSCs. Our study provides experimental evidence for the application of GA in the treatment of cognitive deficits induced by Alzheimer's disease, stroke, or traumatic brain injury.