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. 2019 Jul 30;28(1):74–82. doi: 10.4062/biomolther.2019.024

β-Amyrin Ameliorates Alzheimer’s Disease-Like Aberrant Synaptic Plasticity in the Mouse Hippocampus

Hye Jin Park 1,†, Huiyoung Kwon 1,†, Ji Hye Lee 2,†, Eunbi Cho 1, Young Choon Lee 1,3, Minho Moon 4, Mira Jun 3,5, Dong Hyun Kim 1,3,*, Ji Wook Jung 6,*
PMCID: PMC6939697  PMID: 31357749

Abstract

Alzheimer’s disease (AD) is a progressive and most frequently diagnosed neurodegenerative disorder. However, there is still no drug preventing the progress of this disorder. β-Amyrin, an ingredient of the surface wax of tomato fruit and dandelion coffee, is previously reported to ameliorate memory impairment induced by cholinergic dysfunction. Therefore, we tested whether β-amyrin can prevent AD-like pathology. β-Amyrin blocked amyloid β (Aβ)-induced long-term potentiation (LTP) impairment in the hippocampal slices. Moreover, β-amyrin improved Aβ-induced suppression of phosphatidylinositol-3-kinase (PI3K)/Akt signaling. LY294002, a PI3K inhibitor, blocked the effect of β-amyrin on Aβ-induced LTP impairment. In in vivo experiments, we observed that β-amyrin ameliorated object recognition memory deficit in Aβ-injected AD mice model. Moreover, neurogenesis impairments induced by Aβ was improved by β-amyrin treatment. Taken together, β-amyrin might be a good candidate of treatment or supplement for AD patients.

Keywords: β-amyrin, Amyloid β, Alzheimer’s disease, Synaptic plasticity

INTRODUCTION

Alzheimer’s disease (AD) is a progressive and degenerative brain disease with dementia (Dubois et al., 2007). Although early studies found that senile plaques, aggregations of amyloid β (Aβ), and tangles, aggregations of tau protein, are the major hallmarks of AD and they could induce AD-like pathology (Selkoe, 1991), pharmacological prevention or supplements of AD progression are still not developed.

Aβ, which can be produced by the cleavage of amyloid precursor protein, a membrane protein, is toxic when it is aggregated into oligomeric and fibril forms (Hardy and Selkoe, 2002; Viola and Klein, 2015). Extracellular oligomeric Aβ can bind to various receptors and ion channels, resulting in their dysfunction (Hardy and Selkoe, 2002; Viola and Klein, 2015). Moreover, oligomeric Aβ can penetrate into intracellular space and cause dysfunction of various intracellular signaling systems (Hardy and Selkoe, 2002; Viola and Klein, 2015). These various dysfunctions induce neuronal and synaptic dysfunction resulting in dementia (Hardy and Selkoe, 2002; Viola and Klein, 2015). Therefore, an agent that can prevent Aβ-induced dysfunction of various neuronal functions could be developed as a treatment or supplement for preventing the progression of AD.

Oligomeric Aβ is reported to induce aberrant synaptic plasticity, a cellular model of learning and memory (Walsh et al., 2002). Oligomeric Aβ blocks long-term potentiation (LTP) and facilitates long-term depression (LTD). Previous findings indicated that agents preventing Aβ-induced aberrant synaptic plasticity could ameliorate AD-like pathologies, including memory impairment (Fu et al., 2014; Yan et al., 2016). Therefore, trials to find agents that can modulate Aβ-induced aberrant synaptic plasticity could be a good method for finding medicines or supplements for AD.

β-Amyrin is natural chemical compound of the triterpene class. β-Amyrin is widely distributed in plants and is a component of glycyrrhizin, which is a major bioactive compound with a wide range of pharmacological properties and is used worldwide as a natural sweetener. Moreover, β-amyrin is also present in the surface wax of the tomato fruit (Szakiel et al., 2012). Previous studies revealed that β-amyrin has anti-fibrotic effects on liver injury models (Krishnan et al., 2014; Thirupathi et al., 2017), and anti-inflammatory (Okoye et al., 2014), anti-diabetic (Nair et al., 2014), anti-hyperglycemic, and hypolipidemic effects (Maurya et al., 2012; Santos et al., 2012). Moreover, β-amyrin induces angiogenesis (Ishii et al., 2015). Recent findings indicated that β-amyrin has neurological effects including regulating sleep (Jeon et al., 2015), memory (Park et al., 2014), and nociception (da Silva et al., 2011; Chicca et al., 2012). However, the effect of β-amyrin on AD has not been studied before. In the present study, we tested whether β-amyrin has anti-AD effects using electrophysiological and behavioral studies. Minocycline is a broad-spectrum tetracycline antibiotic drug. Although minocycline has various side effects in clinical uses, various reports suggested minocycline as potential therapeutics with various positive effects in AD models (Noble et al., 2009; Ferretti et al., 2012; Amani et al., 2019). Therefore, we used minocycline as positive control.

MATERIALS AND METHODS

Materials

Aβ was purchased from AnaSpec (CA, USA). Anti-phospho-phosphatidylinositol-3-kinase (pPI3K), PI3K, phosphor-Akt (pAkt), and Akt antibodies were obtained from Cell Signaling Technology (MA, USA). β-amyrin and anti-glyceraldehyde 3-phosphate dehydrogenase (GAPDH) antibody were obtained from Santa Cruz Biotechnology (Santa Cruz, CA, USA). LY294002 and U0126 were obtained from Tocris Bioscience (MO, USA).

Animals

We obtained male CD-1 mice (26–28 g, 6 weeks old) from SAMTAKO biokorea (Osan, Korea). Mice were housed in an animal facility for 1 week prior to the study for adaptation to the new environment. Four mice were kept in a cage and allowed free access to water and food (temperature: 23 ± 1°C, humidity: 60 ± 10%). The lights were on from 07:00 to 19:00. The institutional Animal Care and Use Committee of Dong-A University approved protocols for all animal experiments. All animal experiments followed the National Institutes of Health guide for the care and use of Laboratory animals (NIH Publications No. 8023, revised 1978).

Hippocampal slice preparation and field EPSP recording

Artificial cerebrospinal fluid (ACSF) was comprised of 124 mM NaCl, 3 mM KCl, 26 mM NaHCO3, 1.25 mM NaH2PO4, 2 mM CaCl2, 1 mM MgSO4, and 10 mM D-glucose. We rapidly removed the brain and isolated the mouse hippocampus. Mouse hippocampal tissues were sliced using a McIlwain tissue chopper. 400-μm-thick hippocampal slices were made and incubated in ACSF (20–25°C) for 1 h before the experiment.

Field potential responses were recorded in the Schaffer collateral-commissural pathway in area CA1. Stimuli (constant voltage) were delivered at 30 s intervals. The slope of the evoked field potential responses (fEPSP) was averaged from four consecutive recordings evoked at 30 s intervals. To induce LTP, two trains of high frequency stimulation (HFS: 100 Hz, 100 pulses in 1 s, 30 s interval) were introduced at 20 min after the initiation of a stable baseline. LTP was quantified by comparing the mean fEPSP slope at 80 min after the HFS period with the mean fEPSP slope during the baseline period and calculating the percentage change from the baseline. For the experiments, slices were incubated in ACSF containing vehicle or drugs for 30 min, and then further incubated in ACSF containing Aβ (1 μM) and/or drugs for 2 h before recording.

Western blot

Hippocampal slices were incubated in β-amyrin-containing ACSF for 30 min. Then the slices were further incubated in Aβ and β-amyrin-containing ACSF for 2 h. Afterwards hippocampal slices were homogenized in ice-chilled M-PER buffer (Thermo, Rockford, IL, USA), a containing protease inhibitor, and phosphatase inhibitor cocktail (Thermo). Debris was removed by microcentrifugation (4200×g, 20 min). Proteins from whole-cell lysates were quantified using a BCA protein assay kit following the manufacturer’s instructions. Samples (30 μg of protein) were then subjected to SDS-PAGE (12% gel) under reducing conditions. Proteins were transferred to PDVF membranes using transfer buffer (25 mM Tris-HCl, pH 7.4 containing 192 mM glycine and 20% v/v methanol) at 400 mA for 2 h (4°C). Next, blots were incubated for 2 h with blocking solution (5% skimmed milk for total proteins, 5% BSA for phosphorylated proteins) and then placed at 4°C overnight with 1:1000 dilutions of primary antibody. After serial washing, blots were incubated with a 1:5000 dilution of horseradish peroxidase-conjugated secondary antibody (Santa Cruz Biotechnology) for 1 h at room temperature.

Aβ injection and drug administration

We added 1.0% NH4OH directly to the Aβ1–42 (35–40 μl to 0.5 mg peptide or 70–80 μl to 1 mg peptide). This solution was immediately diluted with 1X phosphate-buffered saline (PBS) to a concentration of 1 mg/ml. The solution was gently vortexed and sonicated at room temperature until fully miscible. Aβ1–42 (10 μM) was incubated at 37°C for 24 h to obtain various soluble oligomeric species, and then 5 μl of Aβ or vehicle (PBS) was acutely injected into the left lateral ventricle by hand (Kim et al., 2016). β-Amyrin (4 mg/kg, p.o.) and vehicle (10% tween 80 solution) was administered from 1 day to 5 day after the Aβ injection (Park et al., 2014). Minocycline (30 mg/kg, i.p.) was used as a positive control (Jiang et al., 2015).

Behavioral tests

Object recognition test: Mice were habituated to the open field (25 cm×25 cm×25 cm) with an internal cue on one of the four walls for 10 min. Thirty minutes after the habituation; mice were re-placed in the same box with two distinct objects. The objects consisted of a glass box and a plastic cylinder. Mice were allowed to freely explore the objects freely for 10 min. After 2 h, mice were placed back in the same box for the test phase. The two objects were again present, but one object was now displaced to a novel spatial location. Mice were allowed to freely explore the environment and the objects for 5 min. Time spent exploring the displaced and non-displaced objects were measured. A preference ratio was calculated using the following formula: Tdisplaced or Tnon-displaced/(Tdisplaced+Tnon-displaced)× 100, where Tdisplaced is the time spent exploring the displaced object and Tnon-displaced denotes the time spent exploring the non-displaced object.

Passive avoidance test: We conducted passive avoidance test using shuttle box, which is composed of separated dark and illuminating rooms. There was guillotine door between rooms. In a training trial, mouse was located in the illuminating room and then guillotine door was opened 10 s later. When the mouse entered the dark room through the guillotine door, the door closed and an electric shock (0.5 mA for 3 s) was delivered through grid floor (training trial). The following day, mouse was re-introduced in illuminating room. Step-through latency to enter the dark room was measured for a period of 300 s (test trial).

Tissue preparation and immunohistochemistry

Immediately after the behavioral tests, we rapidly removed the brain and washed it with phosphate buffer (100 mM, pH 7.4). The brains were fixed in phosphate buffer (50 mM, pH 7.4) containing 4% paraformaldehyde overnight, then immersed in 30% sucrose solution (in 50 mM PBS) and stored at 4°C until sectioning. Frozen sections were prepared in the coronal plane (30 μm) using a cryostat (Leica, Nussloch, Germany) and kept in storage solution (30% ethylene glycol and 30% glycerol in DW) at 4°C. Forty-five sections were obtained from each mouse. Five sections separated by 9-section intervals (270 μm) were used for each immunohistochemical analysis.

For immunohistochemistry, sections were incubated with blocking solution for 2 h, then with goat anti-doublecortin (DCX, 1:500, Santa Cruz Biotechnology) or rat anti-Ki67 (1:500, Santa Cruz Biotechnology) antibody overnight at 4°C. After washing in PBS, the sections were incubated with biotinylated secondary antibody (1:200 dilution, Vector Laboratories, Inc., Burlingame, CA, USA) for 2 h at room temperature and then with avidin-biotin-peroxidase complex (1:100 dilution, Vector). Thereafter, they were reacted with 0.02% 3,3′-diaminobenzidine and 0.01% H2O2 for about 3 min. After each incubation step, the sections were washed three times with PBS. Finally, they were mounted on gelatin-coated slides, dehydrated in ascending alcohol concentrations, and cleared in xylene.

The DCX- or Ki67-positive cells in the SGZ region of the hippocampus were quantified in 5 sections from each mouse by an experimenter who was blind to the identities of the treatment groups. Cell quantification was performed on each marker that was almost entirely included in the section throughout the z-axis at 100× magnification (the average cell diameter was ∼8 μm, and cells <4 μm in diameter were ignored). The average number of immunopositive cells per section was normalized for the entire hippocampus by multiplying this average by the number of 30 μm sections (50 sections) corresponding to the entire hippocampus.

Statistics

Values are expressed as the mean ± SD. Data were analyzed by one-way analysis of variance (ANOVA) followed by Tukey’s post hoc test for multiple comparisons and t-test for single comparisons. For the inhibition study, two-way ANOVA followed by Bonferroni post hoc test. Statistical significance was set at p<0.05.

RESULTS

β-Amyrin blocked Aβ-induced synaptic dysfunction

Impairment of synaptic function is shown in the early phase of AD. Oligomeric Aβ plays important role in this phenomenon. Therefore, we tested the effect of β-amyrin on oligomeric Aβ-induced LTP impairments in the hippocampal tissues. Before the experiment, we found that β-amyrin did not affect basal LTP in normal hippocampal slices (Fig. 1). In the Aβ-treated experiments (Fig. 2A), although LTP was induced by HFS in control slices, HFS failed to induce LTP in the oligomeric Aβ-treated slices, suggesting that oligomeric Aβ impairs synaptic function in the hippocampus (Fig. 2B). Pretreatment with β-amyrin ameliorated Aβ-induced LTP impairments in a concentration dependent manner (Fig. 2C–2E). Moreover, minocycline, a positive control, ameliorated Aβ-induced LTP impairments (Fig. 2F). One-way ANOVA revealed that there is a significant group effect in this experiment (F5,36=8.072, p<0.05, n=7/group, Fig. 2G). These results suggest that β-amyrin ameliorates Aβ-induced LTP impairments.

Fig. 1.

Fig. 1.

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The effect of β-amyrin on hippocampal long-term potentiation (LTP). LTP was measured in Schaffer-collateral pathway of the hippocampus. β-amyrin was pretreated for 2 h to hippocampal slices. Data represent as mean ± SD (n=7/group).

Fig. 2.

Fig. 2.

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The effect of β-amyrin on amyloid β (Aβ)-induced LTP impairment. LTP was measured in Schaffer-collateral pathway of the hippocampus. (A) Experimental schedule. (B) Effect of Aβ (1 μM) on hippocampal LTP. (C) Effect of β-amyrin (1 μM) on Aβ-induced LTP impairment. (D) Effect of β-amyrin (10 μM) on Aβ-induced LTP impairment. (E) Effect of β-amyrin (100 μM) on Aβ-induced LTP impairment. (F) Effect of minocycline (1 μM) on Aβ-induced LTP impairment. (G) Bar chart of normalized fEPSP slop at 80 min time points of each groups. Data represent as mean ± SD (n=7/group). *p<0.05 vs. control group. &p<0.05 vs. Aβ-treated group.

β-Amyrin ameliorated established LTP impairment induced by Aβ

AD patients already have Aβ deposits in their brain and established synaptic dysfunction. Therefore, if drugs can be developed for AD patients, the drug should overcome this established synaptic dysfunction. To test this, we examined the effect of delayed treatment with β-amyrin on established LTP impairment induced by Aβ (Fig. 3A). Two-hour incubation of hippocampal slices with Aβ blocked LTP induction. However, delayed treatment with β-amyrin improved LTP (t12=3.177, p<0.05, n=7/group, Fig. 3B). This suggests that β-amyrin restores LTP after established impairment by Aβ.

Fig. 3.

Fig. 3.

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Effect of delayed treatment of β-amyrin on established LTP impairment induced by amyloid β (Aβ). (A) Experimental schedule. (B) The effect of β-amyrin (100 μM) on established LTP impairment induced by Aβ (1 μM). Data represent as mean ± SD (n=7/group).

PI3K/Akt signaling was involved in the effect of β-amyrin

A previous study reported that glycogen synthase kinase-3β (GSK-3β) inhibitors ameliorated established LTP impairment in an AD model (Jo et al., 2011). Moreover, Aβ impairs PI3K/Akt signaling, an upstream regulator of GSK-3β (Chen et al., 2009; Reddy, 2013). Therefore, we next tested the effect of β-amyrin on PI3K/Akt signaling. As in previous reports, Aβ decreased the activities of PI3K and Akt, which were shown by decreases in their phosphorylation levels (Fig. 4A, 4B, 4D, 4E). β-Amyrin (30 μM) ameliorated the Aβ-induced reduction of PI3K/Akt signaling (PI3K: F2,9=4.543, p<0.05, n=4/group, Fig. 4A, 4B; pAkt: F2,9=8.438, p<0.05, n=4/group, Fig. 4D, 4E). Total forms of PI3K and Akt were not changed by treatment (PI3K: F2,9=0.05842, p>0.05, n=4/group, Fig. 4A, 4C; Akt: F2,9=1.622, p<0.05, n=4/group, Fig. 4D, 4F). These results suggest that β-amyrin ameliorates Aβ-induced abnormality of PI3K/Akt signaling.

Fig. 4.

Fig. 4.

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Effect of β-amyrin on phosphatidylinositol-3-kinase (PI3K)/Akt pathway. Hippocampal slices were incubated in β-amyrin (100 μM)-containing artificial cerebrospinal fluid (ACSF) for 30 min. Then the slices were more incubated in amyloid β (Aβ) (1 μM) and β-amyrin (100 μM)-containing ACSF for 2 h. (A) PI3K signaling. (B) Quantitative analysis of the level of pPI3K compared to glyceraldehyde 3-phosphate dehydrogenase (GAPDH). (C) Quantitative analysis of the level of PI3K compared to GAPDH. (D) Akt signaling. (E) Quantitative analysis of the level of pAkt compared to GAPDH. (F) Quantitative analysis of the level of Akt compared to GAPDH. Data represent as mean ± SD (n=4/group). *p<0.05 vs. control group. #p<0.05 vs. Aβ-treated group.

To confirm these results, we conducted a blocking experiment with the PI3K inhibitor LY294002. Aβ impaired LTP and β-amyrin ameliorated the LTP deficit in the hippocampal slices (Fig. 5A). An off-target inhibitor, U0125 [mitogen-activated protein kinase (MAPK) inhibitor], failed to affect Aβ-impaired LTP and the effect of β-amyrin (two-way ANOVA: U0126, F1,16=1.910, p>0.05; amyrin, F1,16=122.4, p<0.05; interaction, F1,16=0.007 p>0.05, n=5/group, Fig. 5A, 5B). However, LY294002 blocked the effect of β-amyrin (two-way ANOVA: LY294002, F1,16=77.95, p<0.05; amyrin, F1,16=62.15, p<0.05; interaction, F1,16=57.79 p<0.05, n=5/group, Fig. 5C, 5D). These results suggest that β-amyrin ameliorates Aβ-induced LTP impairment through PI3K/Akt signaling.

Fig. 5.

Fig. 5.

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Effect of phosphatidylinositol-3-kinase (PI3K) inhibitor on the effect of β-amyrin on amyloid β (Aβ)-induced LTP impairment. Hippocampal slices were incubated in β-amyrin (100 μM) and inhibitor (U0126 or LY294002)-containing artificial cerebrospinal fluid (ACSF) for 30 min. Then the slices were more incubated in Aβ (1 μM) and β-amyrin (100 μM)-containing ACSF for 2 h. (A, B) Effect of U0126 (20 μM) on the effect of β-amyrin. (A) Field excitatory postsynaptic potential (fEPSP) at every time points. (B) fEPSP at 80 m point. (C, D) Effect of LY294002 (50 μM) on the effect of β-amyrin. (C) fEPSP at every time points. (D) fEPSP at 80 m point. Data represent as mean ± SD (n=5/group). *p<0.05 vs. Aβ-treated group.

β-Amyrin ameliorated memory impairments induced by Aβ

To test whether β-amyrin ameliorates memory impairments induced by Aβ, we tested the effect of β-amyrin on memory impairments in an Aβ-injected mouse AD model (Fig. 6A). Aβ-injected mice showed memory impairments in an object recognition test (Fig. 6B). However, β-amyrin (4 mg/kg, p.o.) ameliorated Aβ-induced memory impairments in the object recognition test (Fig. 6B). Minocycline (30 mg/kg, i.p.), a positive control, also ameliorated memory impairments induced by Aβ (F3,36=2.657, p<0.05, n=10/group, Fig. 6B). During the tests, the total duration of exploration was not different among groups (F3,36=0.04404, p>0.05, n=10/group, Fig. 6C). In the training trial of passive avoidance test, there was no significant difference of the step-through latency between groups (p>0.05, Fig. 6D). However, β-amyrin or minocycline ameliorated memory impairment induced by Aβ (F3,36=9093, p<0.05, n=10/group, p<0.05, Fig. 6E). These results suggest that β-amyrin ameliorates Aβ-induced memory impairments.

Fig. 6.

Fig. 6.

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Effect of β-amyrin on amyloid β (Aβ)-induced memory impairments. β-amyrin (4 mg/kg/day, p.o.) or minocycline (30 mg/kg/day, i.p.) was administered from 1 day after the Aβ (10 μM/5 μl, i.c.v.) injection for 5 days. (A) Experimental schedule. (B) Discrimination ration in object recognition test. (C) Total exploration time in test session of object recognition test. (D) Step-through latency in training trials of passive avoidance test. (E) Step-through latency in test trials of passive avoidance test. Data represent as mean ± SD (n=10/group). *p<0.05 vs. control group. §p<0.05 vs. Aβ-treated group. ORM, object recognition memory test. PAT, passive avoidance test.

β-Amyrin ameliorated neurogenesis impairments induced by Aβ

PI3K/Akt signaling plays an important role in adult neurogenesis, which is aberrantly regulated in the AD brain (Mu and Gage, 2011; Rodriguez and Verkhratsky, 2011; Kitagishi et al., 2014). Therefore, we examined neurogenesis in the hippocampus of Aβ-injected AD model mice with immunohistochemistry with DCX, an immature neuron marker, and Ki67, a proliferation marker. As in previous reports, Aβ treatment decreased neurogenesis, which was confirmed by a reduction of the number of DCX- and Ki67-positive cells in the hippocampus (Fig. 7) (Haughey et al., 2002). β-Amyrin (4 mg/kg, p.o.) and minocycline (30 mg/kg, i.p.) ameliorated the reduction of neurogenesis in our AD model (DCX: F3,16=4.589, p<0.05, n=5/group, Fig. 7A; Ki67: F3,36=4.990, p<0.05, n=5/group, Fig. 7B). These results suggest that β-amyrin ameliorates the Aβ-induced reduction in hippocampal neurogenesis.

Fig. 7.

Fig. 7.

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Effect of β-amyrin on amyloid β (Aβ)-induced neurogenesis impairment. (A) Photomicroscopies and quantitative analysis of double-cortin (DCX)-positive cells in the hippocampus. (B) Photomicroscopies and quantitative analysis of Ki67-positive cells in the hippocampus. Bar=150 μm. Data represent as mean ± SD (n=5/group). *p<0.05 vs. control group. #p<0.05 vs. Aβ-treated group.

DISCUSSION

In the present study, we found that β-amyrin ameliorated Aβ-induced synaptic dysfunction. PI3K inhibition blocked the effect of β-amyrin, suggesting that β-amyrin ameliorates Aβ-induced synaptic dysfunction through the PI3K/Akt pathway. Moreover, delayed β-amyrin administration improved memory impairments and the reduction of hippocampal neurogenesis induced by Aβ injection.

Hippocampal LTP is the enhancement of synaptic efficacy. Many findings suggest that hippocampal LTP is the cellular basis of learning and memory (Nabavi et al., 2014; Penn et al., 2017; Shimshek et al., 2017). In various pathological situations including AD, Parkinson’s disease and stroke, hippocampal LTP is aberrantly regulated (Stein et al., 2015; Tozzi et al., 2015; Zhu et al., 2015). Therefore, regulation of hippocampal LTP might be a candidate means of treating these pathological conditions. Aβ causes over-activation of the NMDA receptor, and results in synaptic dysfunction and cell death (Birnbaum et al., 2015; Arbel-Ornath et al., 2017). Recent findings indicated that activation of PI3K/Akt signaling could prevent various Aβ-induced various pathological conditions (Tiwari et al., 2015; Yi et al., 2018). PI3K/Akt activation inhibits GSK-3β, a key molecule for Aβ-induced synaptic dysfunction (Beurel et al., 2015), and rescues aberrant synaptic plasticity and cell death by Aβ (Yi et al., 2018). A previous report suggested that β-amyrin activates extracellular signal-regulated kinase (ERK) and inhibits GSK-3β in the presence of scopolamine (Park et al., 2014). In the present study, we found that β-amyrin activates PI3K/Akt in the presence of Aβ (Fig. 4). However, blockade of PI3K/Akt prevented an Aβ-induced LTP deficit, but ERK prevention failed. These results suggest that β-amyrin prevents Aβ-induced LTP deficits through PI3K/Akt activation. Interestingly, the present results show that β-amyrin restored established LTP impairment by Aβ. This suggests that β-amyrin might be a disease-modifying drug. A previous study indicated that regulation of GSK-3β could restore Aβ-induced LTP deficits (Jo et al., 2011). Because β-amyrin regulated PI3K/Akt signaling in the present study and GSK-3β activity in previous study (Park et al., 2014), the effect of β-amyrin on an established LTP deficit seems to be due to its effect on PI3K/Akt/GSK-3β signaling. To test this in an in vivo system, we examined the effect of delayed administration of β-amyrin on memory impairments in an AD mouse model. This experiment showed that delayed administration of β-amyrin ameliorated memory impairments in our AD mouse model. These results suggest that β-amylin could be a drug candidate for moderate to severe AD patients. Moreover, according to guidelines for dose conversion between animals and humans (Nair and Jacob, 2016), 4 mg/kg of β-amyrin in mice could be converted to 0.325 mg/kg in humans. However, β-amyrin failed to activate PI3K/Akt signaling in in vivo experiment (data not shown). It could be speculated that β-amyrin may be metabolized in the liver and the metabolite of β-amyrin may act differently in the brain. Further study will be needed to clarify this.

From a functional point of view, hippocampal neurogenesis plays an important role in structural plasticity and network maintenance. Therefore, it is likely to contribute to information storage, as well as learning and memory processes. The hippocampus is affected early in AD. Analysis of post mortem brain tissues from humans clinically diagnosed with AD revealed a reduction of progenitors in the subventricular zone (Ziabreva et al., 2006). Moreover, although it is still controversial, many studies suggested that neurogenic capabilities are impaired in the subgranular zone of the hippocampal DG (Rodriguez et al., 2008; Rodriguez and Verkhratsky, 2011). Voluntary running or environmental enrichment enhanced memory in transgenic mouse models of AD (Rodriguez et al., 2011; Gregoire et al., 2014), as well as increasing hippocampal neurogenesis (Rodriguez et al., 2011; Tapia-Rojas et al., 2016). Moreover, 5-HT facilitation by antidepressants ameliorates AD-like pathology and neurogenesis deficits at late ages (Ma et al., 2017). In the present study, we found that β-amyrin prevents Aβ-induced reduction in neurogenesis. This suggests that β-amyrin might be another therapeutic candidate for AD.

Acknowledgments

This study was supported by the Korea Small and Medium Business Administration (Grant No. S2230716) and BB21+ project in 2018.

REFERENCES

  1. Amani M, Shokouhi G, Salari AA. Minocycline prevents the development of depression-like behavior and hippocampal inflammation in a rat model of Alzheimer’s disease. Psychopharmacology (Berl.) 2019;236:1281–1292. doi: 10.1007/s00213-018-5137-8. [DOI] [PubMed] [Google Scholar]
  2. Arbel-Ornath M, Hudry E, Boivin JR, Hashimoto T, Takeda S, Kuchibhotla KV, Hou S, Lattarulo CR, Belcher AM, Shakerdge N, Trujillo PB, Muzikansky A, Betensky RA, Hyman BT, Bacskai BJ. Soluble oligomeric amyloid-beta induces calcium dyshomeostasis that precedes synapse loss in the living mouse brain. Mol. Neurodegener. 2017;12:27. doi: 10.1186/s13024-017-0169-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Beurel E, Grieco SF, Jope RS. Glycogen synthase kinase-3 (GSK3): regulation, actions, and diseases. Pharmacol. Ther. 2015;148:114–131. doi: 10.1016/j.pharmthera.2014.11.016. [DOI] [PMC free article] [PubMed] [Google Scholar]
  4. Birnbaum JH, Bali J, Rajendran L, Nitsch RM, Tackenberg C. Calcium flux-independent NMDA receptor activity is required for Abeta oligomer-induced synaptic loss. Cell Death Dis. 2015;6:e1791. doi: 10.1038/cddis.2015.160. [DOI] [PMC free article] [PubMed] [Google Scholar]
  5. Chen TJ, Wang DC, Chen SS. Amyloid-beta interrupts the PI3K-Akt-mTOR signaling pathway that could be involved in brain-derived neurotrophic factor-induced Arc expression in rat cortical neurons. J. Neurosci. Res. 2009;87:2297–2307. doi: 10.1002/jnr.22057. [DOI] [PubMed] [Google Scholar]
  6. Chicca A, Marazzi J, Gertsch J. The antinociceptive triterpene beta-amyrin inhibits 2-arachidonoylglycerol (2-AG) hydrolysis without directly targeting cannabinoid receptors. Br. J. Pharmacol. 2012;167:1596–1608. doi: 10.1111/j.1476-5381.2012.02059.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. da Silva KA, Paszcuk AF, Passos GF, Silva ES, Bento AF, Meotti FC, Calixto JB. Activation of cannabinoid receptors by the pentacyclic triterpene alpha,beta-amyrin inhibits inflammatory and neuropathic persistent pain in mice. Pain. 2011;152:1872–1887. doi: 10.1016/j.pain.2011.04.005. [DOI] [PubMed] [Google Scholar]
  8. Dubois B, Feldman HH, Jacova C, Dekosky ST, Barberger-Gateau P, Cummings J, Delacourte A, Galasko D, Gauthier S, Jicha G, Meguro K, O’Brien J, Pasquier F, Robert P, Rossor M, Salloway S, Stern Y, Visser PJ, Scheltens P. Research criteria for the diagnosis of Alzheimer’s disease: revising the NINCDS-ADRDA criteria. Lancet Neurol. 2007;6:734–746. doi: 10.1016/S1474-4422(07)70178-3. [DOI] [PubMed] [Google Scholar]
  9. Ferretti MT, Allard S, Partridge V, Ducatenzeiler A, Cuello AC. Minocycline corrects early, pre-plaque neuroinflammation and inhibits BACE-1 in a transgenic model of Alzheimer’s disease-like amyloid pathology. J. Neuroinflammation. 2012;9:62. doi: 10.1186/1742-2094-9-62. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Fu AK, Hung KW, Huang H, Gu S, Shen Y, Cheng EY, Ip FC, Huang X, Fu WY, Ip NY. Blockade of EphA4 signaling ameliorates hippocampal synaptic dysfunctions in mouse models of Alzheimer’s disease. Proc. Natl. Acad. Sci. U.S.A. 2014;111:9959–9964. doi: 10.1073/pnas.1405803111. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Gregoire CA, Bonenfant D, Le Nguyen A, Aumont A, Fernandes KJ. Untangling the influences of voluntary running, environmental complexity, social housing and stress on adult hippocampal neurogenesis. PLoS ONE. 2014;9:e86237. doi: 10.1371/journal.pone.0086237. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Hardy J, Selkoe DJ. The amyloid hypothesis of Alzheimer’s disease: progress and problems on the road to therapeutics. Science. 2002;297:353–356. doi: 10.1126/science.1072994. [DOI] [PubMed] [Google Scholar]
  13. Haughey NJ, Nath A, Chan SL, Borchard AC, Rao MS, Mattson MP. Disruption of neurogenesis by amyloid beta-peptide, and perturbed neural progenitor cell homeostasis, in models of Alzheimer’s disease. J. Neurochem. 2002;83:1509–1524. doi: 10.1046/j.1471-4159.2002.01267.x. [DOI] [PubMed] [Google Scholar]
  14. Ishii M, Nakahara T, Ikeuchi S, Nishimura M. beta-Amyrin induces angiogenesis in vascular endothelial cells through the Akt/endothelial nitric oxide synthase signaling pathway. Biochem. Biophys. Res. Commun. 2015;467:676–682. doi: 10.1016/j.bbrc.2015.10.085. [DOI] [PubMed] [Google Scholar]
  15. Jeon SJ, Park HJ, Gao Q, Lee HE, Park SJ, Hong E, Jang DS, Shin CY, Cheong JH, Ryu JH. Positive effects of beta-amyrin on pentobarbital-induced sleep in mice via GABAergic neurotransmitter system. Behav. Brain Res. 2015;291:232–236. doi: 10.1016/j.bbr.2015.05.005. [DOI] [PubMed] [Google Scholar]
  16. Jiang Y, Liu Y, Zhu C, Ma X, Ma L, Zhou L, Huang Q, Cen L, Pi R, Chen X. Minocycline enhances hippocampal memory, neuroplasticity and synapse-associated proteins in aged C57 BL/6 mice. Neurobiol. Learn. Mem. 2015;121:20–29. doi: 10.1016/j.nlm.2015.03.003. [DOI] [PubMed] [Google Scholar]
  17. Jo J, Whitcomb DJ, Olsen KM, Kerrigan TL, Lo SC, Bru-Mercier G, Dickinson B, Scullion S, Sheng M, Collingridge G, Cho K. Abeta(1–42) inhibition of LTP is mediated by a signaling pathway involving caspase-3, Akt1 and GSK-3beta. Nat. Neurosci. 2011;14:545–547. doi: 10.1038/nn.2785. [DOI] [PubMed] [Google Scholar]
  18. Kim HY, Lee DK, Chung BR, Kim HV, Kim Y. Intracerebroventricular injection of amyloid-beta peptides in normal mice to acutely induce alzheimer-like cognitive deficits. J. Vis. Exp. 2016;(109):e53308. doi: 10.3791/53308. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Kitagishi Y, Nakanishi A, Ogura Y, Matsuda S. Dietary regulation of PI3K/AKT/GSK-3beta pathway in Alzheimer’s disease. Alzheimers Res. Ther. 2014;6:35. doi: 10.1186/alzrt265. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Krishnan K, Mathew LE, Vijayalakshmi NR, Helen A. Anti-inflammatory potential of beta-amyrin, a triterpenoid isolated from Costus igneus. Inflammopharmacology. 2014;22:373–385. doi: 10.1007/s10787-014-0218-8. [DOI] [PubMed] [Google Scholar]
  21. Ma J, Gao Y, Jiang L, Chao FL, Huang W, Zhou CN, Tang W, Zhang L, Huang CX, Zhang Y, Luo YM, Xiao Q, Yu HR, Jiang R, Tang Y. Fluoxetine attenuates the impairment of spatial learning ability and prevents neuron loss in middle-aged APPswe/PSEN1dE9 double transgenic Alzheimer’s disease mice. Oncotarget. 2017;8:27676–27692. doi: 10.18632/oncotarget.15398. [DOI] [PMC free article] [PubMed] [Google Scholar]
  22. Maurya R, Srivastava A, Shah P, Siddiqi MI, Rajendran SM, Puri A, Yadav PP. beta-Amyrin acetate and beta-amyrin palmitate as antidyslipidemic agents from Wrightia tomen-tosa leaves. Phytomedicine. 2012;19:682–685. doi: 10.1016/j.phymed.2012.03.013. [DOI] [PubMed] [Google Scholar]
  23. Mu Y, Gage FH. Adult hippocampal neurogenesis and its role in Alzheimer’s disease. Mol. Neurodegener. 2011;6:85. doi: 10.1186/1750-1326-6-85. [DOI] [PMC free article] [PubMed] [Google Scholar]
  24. Nabavi S, Fox R, Proulx CD, Lin JY, Tsien RY, Malinow R. Engineering a memory with LTD and LTP. Nature. 2014;511:348–352. doi: 10.1038/nature13294. [DOI] [PMC free article] [PubMed] [Google Scholar]
  25. Nair AB, Jacob S. A simple practice guide for dose conversion between animals and human. J. Basic Clin. Pharm. 2016;7:27–31. doi: 10.4103/0976-0105.177703. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Nair SA, Sabulal B, Radhika J, Arunkumar R, Subramoniam A. Promising anti-diabetes mellitus activity in rats of beta-amyrin palmitate isolated from Hemidesmus indicus roots. Eur. J. Pharmacol. 2014;734:77–82. doi: 10.1016/j.ejphar.2014.03.050. [DOI] [PubMed] [Google Scholar]
  27. Noble W, Garwood C, Stephenson J, Kinsey AM, Hanger DP, Anderton BH. Minocycline reduces the development of abnormal tau species in models of Alzheimer’s disease. FASEB J. 2009;23:739–750. doi: 10.1096/fj.08-113795. [DOI] [PubMed] [Google Scholar]
  28. Okoye NN, Ajaghaku DL, Okeke HN, Ilodigwe EE, Nworu CS, Okoye FB. beta-Amyrin and alpha-amyrin acetate isolated from the stem bark of Alstonia boonei display profound anti-inflammatory activity. Pharm. Biol. 2014;52:1478–1486. doi: 10.3109/13880209.2014.898078. [DOI] [PubMed] [Google Scholar]
  29. Park SJ, Ahn YJ, Oh SR, Lee Y, Kwon G, Woo H, Lee HE, Jang DS, Jung JW, Ryu JH. Amyrin attenuates scopolamine-induced cognitive impairment in mice. Biol. Pharm. Bull. 2014;37:1207–1213. doi: 10.1248/bpb.b14-00113. [DOI] [PubMed] [Google Scholar]
  30. Penn AC, Zhang CL, Georges F, Royer L, Breillat C, Hosy E, Petersen JD, Humeau Y, Choquet D. Hippocampal LTP and contextual learning require surface diffusion of AMPA receptors. Nature. 2017;549:384–388. doi: 10.1038/nature23658. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Reddy PH. Amyloid beta-induced glycogen synthase kinase 3beta phosphorylated VDAC1 in Alzheimer’s disease: implications for synaptic dysfunction and neuronal damage. Biochim. Biophys. Acta. 2013;1832:1913–1921. doi: 10.1016/j.bbadis.2013.06.012. [DOI] [PMC free article] [PubMed] [Google Scholar]
  32. Rodriguez JJ, Jones VC, Tabuchi M, Allan SM, Knight EM, LaFerla FM, Oddo S, Verkhratsky A. Impaired adult neurogenesis in the dentate gyrus of a triple transgenic mouse model of Alzheimer’s disease. PLoS ONE. 2008;3:e2935. doi: 10.1371/journal.pone.0002935. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Rodriguez JJ, Noristani HN, Olabarria M, Fletcher J, Somerville TD, Yeh CY, Verkhratsky A. Voluntary running and environmental enrichment restores impaired hippocampal neurogenesis in a triple transgenic mouse model of Alzheimer’s disease. Curr. Alzheimer Res. 2011;8:707–717. doi: 10.2174/156720511797633214. [DOI] [PubMed] [Google Scholar]
  34. Rodriguez JJ, Verkhratsky A. Neurogenesis in Alzheimer’s disease. J. Anat. 2011;219:78–89. doi: 10.1111/j.1469-7580.2011.01343.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  35. Santos FA, Frota JT, Arruda BR, de Melo TS, da Silva AA, Brito GA, Chaves MH, Rao VS. Antihyperglycemic and hypolipidemic effects of alpha, beta-amyrin, a triterpenoid mixture from Protium heptaphyllum in mice. Lipids Health Dis. 2012;11:98. doi: 10.1186/1476-511X-11-98. [DOI] [PMC free article] [PubMed] [Google Scholar]
  36. Selkoe DJ. The molecular pathology of Alzheimer’s disease. Neuron. 1991;6:487–498. doi: 10.1016/0896-6273(91)90052-2. [DOI] [PubMed] [Google Scholar]
  37. Shimshek DR, Bus T, Schupp B, Jensen V, Marx V, Layer LE, Kohr G, Sprengel R. Different forms of AMPA receptor mediated LTP and their correlation to the spatial working memory formation. Front. Mol. Neurosci. 2017;10:214. doi: 10.3389/fnmol.2017.00214. [DOI] [PMC free article] [PubMed] [Google Scholar]
  38. Stein ES, Itsekson-Hayosh Z, Aronovich A, Reisner Y, Bushi D, Pick CG, Tanne D, Chapman J, Vlachos A, Maggio N. Thrombin induces ischemic LTP (iLTP): implications for synaptic plasticity in the acute phase of ischemic stroke. Sci. Rep. 2015;5:7912. doi: 10.1038/srep07912. [DOI] [PMC free article] [PubMed] [Google Scholar]
  39. Szakiel A, Paczkowski C, Pensec F, Bertsch C. Fruit cuticular waxes as a source of biologically active triterpenoids. Phytochem. Rev. 2012;11:263–284. doi: 10.1007/s11101-012-9241-9. [DOI] [PMC free article] [PubMed] [Google Scholar]
  40. Tapia-Rojas C, Aranguiz F, Varela-Nallar L, Inestrosa NC. Voluntary running attenuates memory loss, decreases neuropathological changes and induces neurogenesis in a mouse model of Alzheimer’s disease. Brain Pathol. 2016;26:62–74. doi: 10.1111/bpa.12255. [DOI] [PMC free article] [PubMed] [Google Scholar]
  41. Thirupathi A, Silveira PC, Nesi RT, Pinho RA. beta-Amyrin, a pentacyclic triterpene, exhibits anti-fibrotic, anti-inflammatory, and anti-apoptotic effects on dimethyl nitrosamine-induced hepatic fibrosis in male rats. Hum. Exp. Toxicol. 2017;36:113–122. doi: 10.1177/0960327116638727. [DOI] [PubMed] [Google Scholar]
  42. Tiwari SK, Seth B, Agarwal S, Yadav A, Karmakar M, Gupta SK, Choubey V, Sharma A, Chaturvedi RK. Ethosuximide induces hippocampal neurogenesis and reverses cognitive deficits in an amyloid-beta toxin-induced alzheimer rat model via the phosphatidylinositol 3-kinase (PI3K)/Akt/Wnt/beta-catenin pathway. J. Biol. Chem. 2015;290:28540–28558. doi: 10.1074/jbc.M115.652586. [DOI] [PMC free article] [PubMed] [Google Scholar]
  43. Tozzi A, Sclip A, Tantucci M, de Iure A, Ghiglieri V, Costa C, Di Filippo M, Borsello T, Calabresi P. Region- and age-dependent reductions of hippocampal long-term potentiation and NMDA to AMPA ratio in a genetic model of Alzheimer’s disease. Neurobiol. Aging. 2015;36:123–133. doi: 10.1016/j.neurobiolaging.2014.07.002. [DOI] [PubMed] [Google Scholar]
  44. Viola KL, Klein WL. Amyloid beta oligomers in Alzheimer’s disease pathogenesis, treatment, and diagnosis. Acta Neuropathol. 2015;129:183–206. doi: 10.1007/s00401-015-1386-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  45. Walsh DM, Klyubin I, Fadeeva JV, Cullen WK, Anwyl R, Wolfe MS, Rowan MJ, Selkoe DJ. Naturally secreted oligomers of amyloid beta protein potently inhibit hippocampal long-term potentiation in vivo. Nature. 2002;416:535–539. doi: 10.1038/416535a. [DOI] [PubMed] [Google Scholar]
  46. Yan R, Fan Q, Zhou J, Vassar R. Inhibiting BACE1 to reverse synaptic dysfunctions in Alzheimer’s disease. Neurosci. Biobehav. Rev. 2016;65:326–340. doi: 10.1016/j.neubiorev.2016.03.025. [DOI] [PMC free article] [PubMed] [Google Scholar]
  47. Yi JH, Baek SJ, Heo S, Park HJ, Kwon H, Lee S, Jung J, Park SJ, Kim BC, Lee YC, Ryu JH, Kim DH. Direct pharmacological Akt activation rescues Alzheimer’s disease like memory impairments and aberrant synaptic plasticity. Neuropharmacology. 2018;128:282–292. doi: 10.1016/j.neuropharm.2017.10.028. [DOI] [PubMed] [Google Scholar]
  48. Zhu G, Li J, He L, Wang X, Hong X. MPTP-induced changes in hippocampal synaptic plasticity and memory are prevented by memantine through the BDNF-TrkB pathway. Br. J. Pharmacol. 2015;172:2354–2368. doi: 10.1111/bph.13061. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Ziabreva I, Perry E, Perry R, Minger SL, Ekonomou A, Przyborski S, Ballard C. Altered neurogenesis in Alzheimer’s disease. J. Psychosom. Res. 2006;61:311–316. doi: 10.1016/j.jpsychores.2006.07.017. [DOI] [PubMed] [Google Scholar]

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