Sweroside Ameliorated Memory Deficits in Scopolamine-Induced Zebrafish (Danio rerio) Model: Involvement of Cholinergic System and Brain Oxidative Stress

Abstract

Sweroside is a secoiridoid glycoside and belongs to a large group of naturally occurring monoterpenes with glucose sugar attached to C-1 in the pyran ring. Sweroside can promote different biological activities such as antifungal, antibacterial, hepatoprotective, gastroprotective, sedative and antitumor, antioxidant, and neuroprotective activities. Zebrafish were given sweroside (12.79, 8.35, and 13.95 nM) by immersion once daily for 8 days, along with scopolamine (Sco, 100 μM) 30 min before the initiation of the behavioral testing to cause anxiety and memory loss. Employing the novel tank diving test (NTT), the Y-maze, and the novel object recognition test (NOR), anxiety-like reactions and memory-related behaviors were assessed. The following seven groups (n = 10 animals per group) were used: control, Sco (100 μM), sweroside treatment (2.79, 8.35, and 13.95 nM), galantamine (GAL, 2.71 μM as the positive control in Y-maze and NOR tests), and imipramine (IMP, 63.11 μM as the positive control in NTT test). Acetylcholinesterase activity (AChE) and the antioxidant condition of the brains were also evaluated. The structure of sweroside isolated from Schenkia spicata was identified. Treatment with sweroside significantly improved the Sco-induced decrease of the cholinergic system activity and brain oxidative stress. These results suggest that sweroside exerts a significant effect on anxiety and cognitive impairment, driven in part by the modulation of the cholinergic system activity and brain antioxidant action.

Keywords: Schenkia spicata; cholinergic function; memory; oxidative stress; scopolamine; sweroside; zebrafish.

Figure 1

NTT results for sweroside (2.79, 8.35, and 13.95 nM). (A) Representative tracking locomotion patterns in various groups; (B) Number of entries to the top; (C) Time spent in top (s); (D) Average entry duration (s); (E) Total distance traveled (m); (F) Freezing duration (s); and (G) Average velocity (m/s). Data are presented as means ± S.E.M. (n = 10 animals per group). * p < 0.01, ** p < 0.001, *** p < 0.0001, and **** p < 0.00001 (Tukey’s post hoc analyses). Imipramine (IMP, 63.11 μM) was used as a reference positive drug.

Figure 2

Assessment of response to novelty in Sco-treated zebrafish subjected to sweroside treatment at doses of 2.79, 8.35, and 13.95 nM in the Y-maze test. (A) Representative tracking locomotion patterns in various groups; (B) Time spent in the novel arm (% of total arm time); (C) Total distance traveled (m); (D) Turn angle (°). Data are presented as means ± S.E.M. (n = 10 animals per group). * p < 0.01, ** p < 0.001, *** p < 0.0001, and **** p < 0.00001 (Tukey’s post hoc analyses). Galantamine (GAL, 2.71 μM) was used as a reference positive drug.

Figure 3

Evaluation of recognition memory in Sco-treated zebrafish subjected to sweroside treatment at doses of 2.79, 8.35, and 13.95 nM in the NOR test: (A) Representative tracking locomotion patterns in various groups; (B) Preference (%). Data are presented as means ± S.E.M. (n = 10 animals per group). *** p < 0.0001 and **** p < 0.00001 (Tukey’s post hoc analyses). Galantamine (GAL, 2.71 μM) was used as reference positive drug.

Figure 4

Effects of sweroside (2.79, 8.35, and 13.95 nM) on (A) AChE; (B) Superoxide dismutase (SOD); (C) Catalase (CAT); (D) glutathione peroxidase (GPX)-specific activities; (E) Reduced glutathione (GSH) and (F) carbonylated protein levels. Data are represented by means ± S.E.M. (n = 10 animals per group). * p < 0.01, ** p < 0.001, *** p < 0.0001, and **** p < 0.00001 (Tukey’s post hoc analyses). Galantamine (GAL, 2.71 μM) was used as a reference positive drug.

Figure 5

Chemical structure of sweroside.