Daphnetin Ameliorates the Amyloid β-Induced Alzheimer Disease via Restoring Potassium-Chloride Co-Transporter 2 (KCC2) Ion Channel Functions in Mice

Abstract

Background: Alzheimer’s disease (AD) is a chronic neurodegenerative disorder characterized by downregulation of potassium voltage-gated channel subfamily a member 2 (KCNA2) proteins. Potassium voltage-gated channel subfamily a member 2 is involved in the regulation of neuronal excitability by restoring neuronal potassium-chloride co-transporter 2 (KCC2) functions. Coumarin derivatives exert neuroprotective effects via upregulation of KCC2 proteins. Daphnetin (DPN; 7,8-dihydroxy coumarin) is a polyphenolic compound known to attenuate cognitive dysfunction. However, the role of DPN in the attenuation of AD-associated cognitive dysfunctions through regulation of KCC2 functions has not yet been investigated. Objectives: The present study was designed to investigate the role of DPN against amyloid-β oligomer-induced AD in mice. Methods: In this study, a total of six groups with eight male Swiss albino mice per group were used. The simple randomization method was adopted for unbiased assignment of animals based on age, sex, and weight variations. Alzheimer’s disease in mice was induced by intracerebroventricular (i.c.v.) injection of amyloid-β oligomer (Aβ; 4 μg/4 μL). The test compounds, i.e., DPN (40, 80, and 120 mg/kg of body weight), and donepezil (DP, 2 mg/kg), were administered orally (p.o.) for 21 consecutive days. Behavioral changes, including the Morris water maze (MWM) test, water Y-maze alternation test (WYMA), and novel object recognition test (NORT), were assessed according to the experimental protocol. Furthermore, hippocampal brain tissue biomarkers, namely acetylcholinesterase (AChE) activity, thiobarbituric acid reactive substances (TBARS), reduced glutathione (GSH), and KCC2 levels, were also estimated. In addition, Aβ-associated brain histopathological changes were evaluated using the eosin and hematoxylin staining method. Six mouse hippocampus tissue samples were used for the assessment of tissue biomarkers, and the remaining two brain tissues were used for histological observations. Behavioral data were statistically analyzed by two-way analysis of variance (ANOVA), and biomarkers were analyzed by one-way ANOVA. The 95% confidence level (P < 0.05) was set for confirmation of statistical significance. Results: The results revealed that administration of Aβ enhanced escape latency time (ELT) and reduced time spent in the target quadrant (TSTQ) values in the MWM test; increased transfer latency (TL) values in the WYMA test; and reduced percentage location preference (%LP) while increasing percentage Recognition Index (%RI) in the NORT test. Furthermore, Aβ induced increases in AChE activity and TBARS levels, along with reductions in GSH and KCC2 levels. It also caused neurodegeneration in the CA3 hippocampus region. However, DPN ameliorated the above Aβ-induced changes in cognitive behaviors, biomarkers, and histopathological levels. Conclusions: Daphnetin attenuates Aβ-associated AD progression via inhibition of AChE activity, scavenging of free radicals, reduction of inflammation, and restoration of neuronal KCC2 channels. Hence, it may be a potential therapeutic agent for the treatment of AD. However, more extensive studies are required to confirm this therapeutic potency in different AD conditions and various animal species.