Inhibition of Glycyrrhiza Polysaccharide on Human Cytochrome P450 46A1 in vitro and in vivo: Implications in Treating Neurological Diseases

Background: Cytochrome P450 (CYP) 46A1, also known as cholesterol 24S-hydroxylase, is essential for maintaining the homeostasis of cholesterol in the brain and serves as a therapeutic target of neurodegenerative disorders and excitatory neurotoxicity. N-methyl-d-aspartate receptor (NMDAR) is a prototypical receptor for the excitatory neurotransmitter glutamate and can be specifically regulated by 24S-hydroxycholesterol (24S-HC). Glycyrrhiza is one of the most widely used herbs with broad clinical applications. It has several pharmacological activities, such as clearing heat and detoxifying, moistening the lung and relieving cough, analgesic, neuroprotective outcomes, and regulating a variety of drug activities. Glycyrrhiza is a commonly used herb for the treatment of epileptic encephalopathy. However, whether glycyrrhiza can interfere with the activity of CYP46A1 remains unknown. Objective: This study aimed to investigate the regulating effects of glycyrrhiza polysaccharides (GP) on CYP46A1-mediated cholesterol conversion, as well as in the modulation of related proteins. Materials and Methods: The effects of glycyrrhiza polysaccharide (GP) on the activity of CYP46A1 were investigated in vivo and in vitro. Moreover, the potential regulatory effects of GP on the expressions of CYP46A1, HMG-CoA reductase (HMGCR), and NMDAR were also detected. Results: The in vitro results demonstrated that glycyrrhiza polysaccharide (GP), as the main water-soluble active component of glycyrrhiza, remarkably inhibited the activity of CYP46A1 in a non-competitive mode with a Ki value of 0.7003 mg/ml. Furthermore, the in vivo experiments verified that GP markedly decreased the contents of 24S-HC in rat plasma and brain tissues as compared to the control. More importantly, the protein expressions of CYP46A1, GluN2A, GluN2B, and HMG-CoA reductase (HMGCR) in rat brains were all downregulated, whereas the mRNA expressions of CYP46A1 and HMGCR were not significantly changed after treatment with GP. Conclusion : GP exhibits a significant inhibitory effect on CYP46A1 activity in vitro and in vivo, and the protein expressions of CYP46A1, HMGCR, and NMDAR are also inhibited by GP, which are of considerable clinical significance for GP's potential therapeutic role in treating neurological diseases.