Anxiolytic and Antidepressant Effects of Tribulus terrestris Ethanolic Extract in Scopolamine-Induced Amnesia in Zebrafish: Supported by Molecular Docking Investigation Targeting Monoamine Oxidase A

Abstract

Plants of the genus Tribulus have been used in folk medicine for wound healing, alleviating liver, stomach, and rheumatism pains, and as cognitive enhancers, sedatives, antiseptics, tonics, and stimulants. The present work aimed to evaluate whether Tribulus terrestris (Tt) administered for 15 days attenuated cognitive deficits and exhibited anxiolytic and antidepressant profiles in scopolamine-induced amnesia in zebrafish. Animals were randomly divided into six groups (eight animals per group): (1)-(3) Tt treatment groups (1, 3 and 6 mg/L), (4) control, (5) scopolamine (SCOP, 0.7 mg/kg), and (6) galantamine (Gal, 1 mg/L). Exposure to SCOP (100 µM) resulted in anxiety in zebrafish, as assessed by the novel tank diving test (NTT) and novel approach test (NAT). When zebrafish were given SCOP and simultaneously given Tt (1, 3, and 6 mg/L once daily for 10 days), the deficits were averted. Molecular interactions of chemical compounds from the Tt fractions with the monoamine oxidase A (MAO-A) were investigated via molecular docking experiments. Using behavioral experiments, we showed that administration of Tt induces significant anxiolytic-antidepressant-like effects in SCOP-treated zebrafish. Our result indicated that flavonoids of Tt, namely kaempferol, quercetin, luteolin, apigetrin, and epigallocatechin, could act as promising phytopharmaceuticals for improving anxiety-related disorders.

Keywords: Alzheimer’s disease; NTT; depression; kaempferol; locomotor activity; monoamine oxidase A.

Figure 1

Novel tank dividing test (NTT) results for Tribulus terrestris (Tt: 1, 3 and 6 mg/L). (A) Representative tracking locomotion patterns; (B) Time spent in the top (s); (C) Distance travelled in the top (m); (D) Number of entries to the top (s); (E) Average entry duration; (F) Freezing duration (s); (G) Latency. Data are expressed as means ± S.E.M. (n = 8). * p < 0.01, ** p < 0.001, *** p < 0.0001, and **** p < 0.00001 (Tukey’s post hoc analyses). Galantamine (GAL, 1 mg/L) was used as a reference positive drug.

Figure 2

Novel approach test (NAT) results for Tribulus terrestris (Tt: 1, 3, and 6 mg/L). (A) Representative tracking locomotion patterns; (B) Immobility (s); (C) Distance travelled (m); (D) latency; (E) Times in zones (s). Data are expressed as means ± S.E.M. (n = 8). * p < 0.01, ** p < 0.001, *** p < 0.0001, and **** p < 0.00001 (Tukey’s post hoc analyses). Galantamine (GAL, 1 mg/L) was used as a reference positive drug.

Figure 3

The root means square deviation (RMSD) between the original and docked poses of the co-crystal ligands for the MAO-A enzyme (PDB: 2z5x) was 0.13 Å.

Figure 4

2D and 3D representation of co-crystal ligand docked into binding site of MAO_A active site enzyme.

Figure 5

2D and 3D representations of Kaempferol docked into binding site of MAO-A active site enzyme.

Figure 6

2D and 3D representations of Quercetin docked into binding site of MAO-A active site enzyme.

Figure 7

2D and 3D of Luteoline docked into binding site of MAO-A active site enzyme.

Figure 8

The experimental design of the study (NTT and NAT test).