Dracocephalum moldavica attenuates scopolamine-induced cognitive impairment through activation of hippocampal ERK-CREB signaling in mice
Graphical abstract
Introduction
Alzheimer's disease (AD) is mainly characterized by memory deficits and mental dysfunction; the former is known to be mainly correlated with declines in cholinergic neurotransmission systems (Francis et al., 1999). Behavioral studies have shown that anti-cholinergic drugs impair cognitive function in healthy humans and animals (Atri et al., 2004; Flood and Cherkin, 1986). Accordingly, blockade of the cholinergic system with muscarinic cholinergic receptor antagonists (e.g. scopolamine) is widely used to induce cognitive impairment (Klinkenberg and Blokland, 2010). Moreover, several synthetic drugs, including cholinesterase inhibitors, have been used for cognitive enhancement. Although synthetic memory-enhancing drugs effectively improve memory performance, they have several adverse effects, such as nausea, vomiting, diarrhea and anorexia (Gauthier, 2001). Thus, many studies have focused on the identification of novel drugs, particularly herbal plants, to treat various neurodegenerative diseases, including AD.
Dracocephalum moldavica L. (Lamiaceae, Labiatae) is a perennial aromatic herb native to central Asia, northern China, and eastern and central Europe, and is commonly referred to as Moldavian balm. Because it is naturally warm and fragrant, D. moldavica can affect the central nervous system (CNS), cardiac tissues, and blood circulation (Liu et al., 2018). Accordingly, D. moldavica has been traditionally used for the treatment of heart disease, blood pressure, angina, atherosclerosis, neuralgia, migraines, headaches and toothaches (Dastmalchi et al., 2007; Liu et al., 2018; Maimaitiyiming et al., 2014; Zhao et al., 2017). Additionally, recent studies have confirmed that D. moldavica has various pharmacological effects on the CNS, such as neuroprotection against rat cerebral ischemia reperfusion injury (Jia et al., 2017; Zeng et al., 2018), anti-oxidative and anti-inflammatory properties in an animal model of AD (Liu et al., 2018) and the promotion of prolonged pentobarbital-induced sleeping time and sedation in mice (Martinez-Vazquez et al., 2012). Furthermore, phytochemical studies have revealed that D. moldavica primarily contains rosmarinic acid, oleanolic acid, chlorogenic acid, ferulic acid, caffeic acid, p-coumaric acid, apigenin, quercetin, acacetin, tilianin and luteolin (Li et al., 2016). We and several groups have reported that scopolamine-induced cognitive impairment is ameliorated by oleanolic acid (Jeon et al., 2017), rosmarinic acid (Qu et al., 2017) and chlorogenic acid (Kwon et al., 2010) which are documented constituents of D. moldavica.
Extracellular signal-regulated kinase (ERK) and cAMP response element-binding protein (CREB) signaling molecules are known to be involved in cognitive functions. ERK belongs to the mitogen-activated protein kinase family member and activates CREB, which regulates cellular processes for the regulation of long-term synaptic plasticity and the stabilization of new memories (Adams and Sweatt, 2002; Kelleher et al., 2004). Multiple studies have confirmed that improvements in cognitive abilities are facilitated by the activation of ERK signaling (Ciccarelli and Giustetto, 2014; Kim et al., 2012). CREB is a transcription factor that binds to the promoter regions of many neuronal genes associated with learning, memory and synaptic plasticity (Alberini, 2009). Thus, the activation of the ERK-CREB signaling cascade is necessary for the formation and storage of memories in the hippocampus. It should be noted that a total flavonoid extract of D. moldavica has been reported to attenuate β-amyloid-induced neurotoxicity through the activation of neurotrophic pathways, including the ERK-CREB-brain-derived neurotrophic factor (BDNF) pathway (Liu et al., 2018).
Based on previous studies, we hypothesized that D. moldavica may cure cognitive disorders by targeting ERK/CREB signaling. However, no reports have described the memory-ameliorating effect of D. moldavica on cognitive impairments due to cholinergic blockade. Hence, the aim of this study was to investigate whether the ethanolic extract of D. moldavica (EEDM) attenuates the scopolamine-induced cognitive impairment in mice using the passive avoidance and Morris water maze tasks. We also investigated whether EEDM affects the phosphorylation levels of ERK and CREB in the hippocampus.
Section snippets
Animals
Male CD1 ICR mice (6 weeks old, 25–30 g) were purchased from the Orient Co. Ltd., a branch of Charles River Laboratories (Seoul, Korea). The mice were housed in groups of 5 per cage, provided with ad libitum access to food and water, and kept under a 12 h light/dark cycle (lights on 07:00–19:00) at a constant temperature (23 ± 1 °C) and relative humidity (60 ± 10%). Animal treatment and maintenance were carried out in accordance with the Principles of Laboratory Animal Care (NIH publication No.
Effects of EEDM on scopolamine-induced memory impairment in the step-through passive avoidance task
To investigate the effects of EEDM on the control mice (Fig. 2A and B), as well as the scopolamine-induced amnesic mice (Fig. 2C and D), the step-through passive avoidance task was conducted after a single administration of EEDM. In the case of the control mice (which were not treated with scopolamine), there were no significant differences in the latencies either in the acquisition or retention trials (one-way ANOVA, acquisition trial, F4, 44 = 0.537, P = 0.709; retention trial, F4, 44
Discussion
In the present study, we first found that EEDM ameliorated scopolamine-induced memory decline in the step-through passive avoidance and Morris water maze tasks. Interestingly, EEDM improved scopolamine-induced cognitive impairment but did not affect the cognitive activity in control mice in the step-through passive avoidance task. It should be noted that EEDM did not cause any changes in motor function, as measured by the swimming speed in the Morris water maze task and the step-through latency
Author's contributions
The study was conceived and designed by J.H.R. and S.J.P. Behavioral studies were conducted by P.D., H.J.B. and H.P. Immunoblotting assays were performed by H.J.B, S.K. and J.W.C. EEDM sample was prepared and standardized by X.L., S.K. and D.H.K. The manuscript was written by P.D., J.H.R. and S.J.P.
Declaration of competing interest
The authors declare that there is no conflict of interest.
Acknowledgments
This study was supported by the National Research Foundation of Korea (NRF) grant funded by the Ministry of Science and ICT (NRF-2017R1C1B5017445; NRF-2017R1A5A2014768) and 2018 Research Grant from Kangwon National University.
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