Tetrandrine Ameliorated Alzheimer’s Disease through Suppressing the Inflammatory Activation of Microglia in 5XFAD Mouse

Abstract Background Alzheimer’s disease is a neurodegenerative disorder prevalent in aged population. Tetrandrine is a natural metabolite isolated from herbal medicine Stephania tetrandra with various activities. Our previous study showed that tetrandrine can ameliorate acute cognitive impairment in a rat model induced by Aβ 1-42 intra-hippocampus injection. In this study, we further investigated the therapeutic role of tetrandrine in the transgenic 5XFAD mouse, a chronic model of Alzheimer’s disease. Methods High performance liquid chromatography (HPLC) was used to determine the distribution of tetrandrine in brain. 5XFAD mice were treated with intraperitoneal injection of saline or tetrandrine (10, 20 and 40 mg/kg per 2 days) for 2 months. Cognitive ability was measured by Morris water maze test. The distribution of amyloid plaque was determined by immunohistochemistry in the brains. The expression of TNFα, IL-1β, IL-6, COX-2, iNOS and NF-κB were quantified by RT-PCR. In vitro , the inflammatory activation of microglial BV2 cells was checked by secretion of TNFα and IL-1β determined by ESLIA. Proinflammatory factors including TLR4, NF-κB, iNOS and COX-2 were analyzed by Western blot. In PC12-derived neural cells, CCK8 assay was used to determine the cell viability. Flow cytometry was applied to quantify cell apoptosis. Immunofluorescence was used to study the expression of apoptosis-involved protein cleaved Caspase-3 and Bcl-2. Results Tetrandrine can be distributed in the brain after intraperitoneal injection. Injection of tetrandrine significantly improved the cognitive ability of 5XFAD mice in the Morris water maze test. 5XFAD mice receiving tetrandrine showed notably reduced deposition of amyloid plaque in the brain and decreased cell apoptosis in the hippocampus. Further, tetrandrine treatment suppressed the expression of pro-inflammatory cytokines (TNFα, IL-1β, IL-6) and inflammation modulator (COX-2, iNOS, NF-κB) in the brain tissue. In vitro , tetrandrine suppressed Aβ 1-42-induced inflammatory activation of microglial BV2 cells as revealed by decreased secretion of TNFα and IL-1β, and inhibited expression of TLR4, NF-κB, iNOS and COX-2. Treatment of PC12-derived neural cells with conditional medium from Aβ 1-42-stimulated BV2 cells remarkably impaired cell viability and promoted cell apoptosis, which was attenuated by tetrandrine pre-treatment of the BV2 cells. Conclusions Tetrandrine improves the Alzheimer’s disease at least partially through suppressing microgrlia-mediated inflammation and neurotoxicity.