Platycodon grandiflorum root extract inhibits Aβ deposition by breaking the vicious circle linking oxidative stress and neuroinflammation in Alzheimer’s disease

Abstract

Alzheimer’s disease (AD) is a progressive neurodegenerative disease accompanied by irreversible cognitive impairment. A deleterious feedback loop between oxidative stress and neuroinflammation in early AD exacerbates AD-related pathology. Platycodon grandiflorum root extract (PGE) has antioxidant and anti-inflammatory effects in several organs. However, the mechanisms underlying the effects of PGE in the brain remain unclear, particularly regarding its impact on oxidative/inflammatory damage and Aβ deposition. Thus, we aim to identify the mechanism through which PGE inhibits Aβ deposition and oxidative stress in the brain by conducting biochemical and histological analyses. First, to explore the antioxidant mechanism of PGE in the brain, we induced oxidative stress in mice injected with scopolamine and investigated the effect of PGE on cognitive decline and oxidative damage. We also assessed the effect of PGE on reactive oxygen species (ROS) generation and the expressions of antioxidant enzymes and neurotrophic factor in H2O2- and Aβ-treated HT22 hippocampal cells. Next, we investigated whether PGE, which showed antioxidant effects, could reduce Aβ deposition by mitigating neuroinflammation, especially microglial phagocytosis. We directly verified the effect of PGE on microglial phagocytosis, microglial activation markers, and pro-inflammatory cytokines in Aβ-treated BV2 microglial cells. Moreover, we examined the effect of PGE on neuroinflammation, inducing microglial responses in Aβ-overexpressing 5XFAD transgenic mice. PGE exerts antioxidant effects in the brain, enhances microglial phagocytosis of Aβ, and inhibits neuroinflammation and Aβ deposition, ultimately preventing neuronal cell death in AD. Taken together, our findings indicate that the therapeutic potential of PGE in AD is mediated by its targeting of multiple pathological processes.

Keywords

• Alzheimer’s disease
• Platycodon grandiflorum
• oxidative stress
• neuroinflammation
• Aβ deposition
• 5XFAD mouse