Lignan-Rich Sesame (Sesamum indicum L.) Cultivar Exhibits In Vitro Anti-Cholinesterase Activity, Anti-Neurotoxicity in Amyloid-β Induced SH-SY5Y Cells, and Produces an In Vivo Nootropic Effect in Scopolamine-Induced Memory Impaired Mice

Abstract

Alzheimer's disease, a major cause of dementia, is characterized by impaired cholinergic function, increased oxidative stress, and amyloid cascade induction. Sesame lignans have attracted considerable attention owing to their beneficial effects on brain health. This study investigated the neuroprotective potential of lignan-rich sesame cultivars. Among the 10 sesame varieties studied, Milyang 74 (M74) extracts exhibited the highest total lignan content (17.71 mg/g) and in vitro acetylcholinesterase (AChE) inhibitory activity (66.17%, 0.4 mg/mL). M74 extracts were the most effective in improving cell viability and inhibiting reactive oxygen species (ROS) and malondialdehyde (MDA) generation in amyloid-β_25-35 fragment-treated SH-SY5Y cells. Thus, M74 was used to evaluate the nootropic effects of sesame extracts and oil on scopolamine (2 mg/kg)-induced memory impairment in mice compared to the control cultivar (Goenback). Pretreatment with the M74 extract (250 and 500 mg/kg) and oil (1 and 2 mL/kg) effectively improved memory disorder in mice (demonstrated by the passive avoidance test), inhibited AChE, and enhanced acetylcholine (Ach) levels. Moreover, immunohistochemistry and Western blot results showed that the M74 extract and oil reversed the scopolamine-induced increase in APP, BACE-1, and presenilin expression levels in the amyloid cascade and decreased BDNF and NGF expression levels in neuronal regeneration.

Keywords: amyloid-β; lignan; neuronal regeneration; neurotoxicity; sesame.

Figure 1

Schematic diagram. (a) Screening of functional compound and in vitro bioactive activities in different sesame varieties, (b) animal experiment design.

Figure 2

Functional compound contents, antioxidant activity, and enzyme inhibitory activity from 10 sesame varieties. Values are the mean ± SD of 3 replicates. Different capital letters and small letters in the same items indicate a significant difference (p < 0.05) among different varieties and extraction concentration, respectively. (a) Functional compound contents: total polyphenol content, total flavonoid content, total lignan content, oil−soluble lignan, soluble lignan (b); (e) individual sesame lignan composition: sesamin, sesamolin, sesaminol, sesaminol-diglucoside, and sesaminol−triglucoside. (c) Antioxidant activities: 2,2′−azino−bis3−ethylbenzothiazoline−6−sulphonic acid (ABTS) radical scavenging activity, 2,2-diphenyl−1−picrylhydrazyl (DPPH) radical scavenging activity. (d) High performance liquid chromatography (HPLC) chromatogram of sesame lignan: (1) sesamin, (2) sesamolin, (3) sesaminol-−triglucoside, (4) sesaminol−diglucoside, (5) sesaminol. (f) Enzyme inhibitory activities: acetylcholinesterase (AChE), butylcholinesterase (BChE), angiotensin converting enzyme (ACE), and α-glucosidase (AG) inhibitory activity. (g) Acetylcholinesterase (AChE) inhibitory activity depending on 10 varieties and extracts concentration (0.1, 0.2, 0.4 mg/g): Goenbaek (GB), Ansan (AS), Koppom (KP), Daheuk (DH), and Milyang 68, 69, 70, 73, 74.

Figure 3

Effect of lignan−rich ‘Milyang 74’ sesame cultivar on neuroprotective activities (25, 50, 100, 200 μg/mL) in amyloid−β−induced SH-SY5Y cell death compared to ‘Goenback’ and ‘Daheuk’ control cultivars. Values are means ± SD of 3 replicates. ^### p < 0.001 significant difference compared to control. Different capital letters and small letters in the same items indicate a significant difference (p < 0.05) among different varieties and extraction concentration, respectively. (a) Cell viability, (b) neuroprotective effect, (c) intracellular reactive oxygen species (ROS) levels, (d) fluorescence intensity for ROS in amyloid−β−induced SH−SY5Y cells. Different capital letters and small letters in the same items indicate a significant difference (p < 0.05) among different cultivars and sample treatment concentrations, respectively.

Figure 4

Effect of lignan−rich sesame cultivar (‘Milyang 74’) and control cultivar (‘Goenback’) pretreatments (sesame extract: 250, 500 mg/kg; sesame oil: 1, 2 mL/kg) on the improvements of impaired memory functions, AChE activity, and ACh concentration in SCOP (scopolamine) −treated ICR mice. Values are means ± SD of 7 replicates. ^### p or *** p < 0.0001, * p < 0.05 significant difference compared to SCOP−treated control. (a) Passive avoidance test, (b) water maze test, (c) acetylcholinesterase activity, (d) acetylcholine concentration.

Figure 5

Effect of lignan-rich sesame cultivar (‘Milyang 74’) and control cultivar (‘Goenback’) pretreatments (sesame extract: 250, 500 mg/kg, sesame oil: 1, 2 mL/kg) on protein expression related to amyloid-β accumulation in mouse brain tissue extract of scopolamine-treated ICR mice. Values are means ± SD of 3 replicates. ^### p or *** p < 0.0001, * p < 0.05 significant difference compared to SCOP-treated control. (a) Western blot analysis of APP, BACE-1, presenilin, and amyloid-β, with GAPDH used as the loading control. (b) Glial fibrillary acidic protein (GFAP), (c) amyloid precursor protein (APP), (d) BACE-1 (e) presenilin, (f) amyloid-β.

Figure 6

Effect of lignan−rich sesame cultivar (‘Milyang 74’) and control cultivar (‘Goenback’) pretreatments (sesame extract: 250, 500 mg/kg, sesame oil: 1, 2 mL/kg) on protein expression related to neuronal regeneration and inflammation. Values are means ± SD of 3 replicates. ^### p or *** p < 0.0001, ^## p or ** p < 0.001, ^# p or * p < 0.05 significant difference compared to SCOP-treated control. (a) Western blot analysis of NGF, BDNF, and COX-2 was performed with GAPDH used as the loading control. (b) NGF, (c) BDNF, (d) COX−2, (e) TNF−α, (f) IL−6, (g) IL−1β.

Figure 6

Effect of lignan−rich sesame cultivar (‘Milyang 74’) and control cultivar (‘Goenback’) pretreatments (sesame extract: 250, 500 mg/kg, sesame oil: 1, 2 mL/kg) on protein expression related to neuronal regeneration and inflammation. Values are means ± SD of 3 replicates. ^### p or *** p < 0.0001, ^## p or ** p < 0.001, ^# p or * p < 0.05 significant difference compared to SCOP-treated control. (a) Western blot analysis of NGF, BDNF, and COX-2 was performed with GAPDH used as the loading control. (b) NGF, (c) BDNF, (d) COX−2, (e) TNF−α, (f) IL−6, (g) IL−1β.