Quinovic Acid Impedes Cholesterol Dyshomeostasis, Oxidative Stress, and Neurodegeneration in an Amyloid-beta-Induced Mouse Model

Abstract

Alzheimer's disease (AD) is a progressive neurodegenerative disorder typified by several neuropathological features including amyloid-beta (A beta) plaque and neurofibrillary tangles (NFTs). Cholesterol retention and oxidative stress (OS) are the major contributors of elevated beta- and gamma-secretase activities, leading to excessive A beta deposition, signifying the importance of altered cholesterol homeostasis and OS in the progression of A beta-mediated neurodegeneration and cognitive deficit. However, the effect of A beta on cholesterol metabolism is lesser-known. In this study, we evaluated the effect of quinovic acid (QA; 50 mg/kg body weight, i.p.) against the intracerebroventricular (i.c.v.) injection of A beta (1-42)-induced cholesterol dyshomeostasis, oxidative stress, and neurodegeneration in the cortex and hippocampal brain regions of wild-type male C57BL/6J mice. Our results indicated that A beta (1-42)-treated mice have increased A beta oligomer formation along with increased beta-secretase expression. The enhanced amyloidogenic pathway in A beta (1-42)-treated mice intensified brain cholesterol accumulation due to increased expressions of p53 and 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR) enzyme. Importantly, we further confirmed the p53-mediated HMGCR axis activation by using pifithrin-alpha (PFT) in SH-SY5Y cells. Furthermore, the augmented brain cholesterol levels were also associated with increased OS. However, the QA administration to A beta (1-42)-injected mice significantly ameliorated the A beta burden, p53 expression, and cholesterol accumulation by deterring the oxidative stress through upregulating the Nrf2/HO-1 pathway. Moreover, the QA downregulated gliosis, neuroinflammatory mediators (p-NF-kappa B and IL-1 beta), and the expression of mitochondrial apoptotic markers (Bax, cleaved caspase-3, and cytochrome c). QA treatment also reversed the deregulated synaptic markers (PSD-95 and synaptophysin) and improved spatial learning and memory behaviors in the A beta-treated mouse brains. These results suggest that A beta (1-42) induces its acute detrimental effects on cognitive functions probably by increasing brain cholesterol levels through a possible activation of the p53/HMGCR axis. However, QA treatment reduces the cholesterol-induced oxidative stress, neuroinflammation, and neurodegeneration, leading to the restoration of cognitive deficit after A beta (1-42) i.c.v. injection in mice.