Chemical Composition, In Silico and In Vitro Antimutagenic Activities of Ethanolic and Aqueous Extracts of Tigernut (Cyperus esculentus)

Abstract

Tigernut, also known as Cyperus esculentus, is said to be high in nutritional and medicinal value. The purpose of this study was to determine the C. esculentus's antimutagenic activity. The ethanolic and aqueous extracts of the nut were analyzed for chemical constituents, antioxidants, ultraviolet-visible, and gas chromatography-mass spectrometry using standard procedures. The extracts contained a total of 17 major compounds that were docked against human RecQ-like protein 5 (RECQL5) helicase protein. The antimutagenic property of the ethanolic extract in vitro was assessed using the Allium cepa chromosome assay. Onion bulbs were pre-treated with 200 mg/kg of ethanolic extract of C. esculentus for 24 h and then, grown in NaN₃ (250 μg/L) for 24 h; onion bulbs were also first exposed to NaN₃ (250 μg/L) for 24 h before treatment with 100 mg/kg and 200 mg/kg of the ethanolic extract respectively. Standard methods were used to determine the mitotic index and chromosomal aberrations. Results revealed that C. esculentus ethanolic extract contained flavonoids (22.47 mg/g), tannins (0.08 mg/g), alkaloids (19.71 mg/g), glycosides, phenol, and tannin and showed high scavenging activity against 2,2-diphenyl-1-picrylhydrazyland H₂O₂. Docking with RECQL5 showed good binding energies (∆G>-7) of five compounds in C. esculentus ethanolic extract. The A. cepa assay results revealed a significant (P<0.05) reduction in chromosomal aberrations and a higher mitotic index in groups treated with the C. esculentus ethanolic extract. The antimutagenic activity of C. esculentus ethanolic extract was attributed to its high levels of phytosterols and phenolic compounds.

Keywords: Allium cepa chromosome assay; Cyperus esculentus; antimutagenic; sodium azide.

Fig. 1

Image of a tigernut (Cyperus esculentus).

Fig. 2

Human RECQL5 protein has a three-dimensional structure (Protein Data Bank ID: 5LB8).

Fig. 3

Ultraviolet-visible spectra of ethanolic and aqueous tigernut extracts.

Fig. 4

Major components in the gas chromatography-mass spectrometry spectra of tigernut ethanolic extract. a, 2,4-di-tert-butylphenol; b, hexadecanoic acid, ethyl ester; c, trans-13-octadecenoic acid; d, octadecanoic acid; e, vitamin E; f, campesterol; g, stigmasterol; h, γ-sitosterol.

Fig. 5

Major components in the gas chromatography-mass spectrometry spectra of tigernut aqueous extract. a, propanenitrile, 3-(methylthio); b, p-dioxane-2,3-diol, ethyl ester; c, 1,2,3,4-butanetetrol; d, cyclotrisiloxane, hexamethyl; e, cyclotetrasiloxane, octamethyl; f, n-hexadecanoic acid; g, bis(trimethylsilyl)benzene; h, boronic acid, ethyl-, bis(2-mercaptoethyl ester); i, n-hexadecanoic acid; j, octadec-9-enoic acid.

Fig. 6

Compound structures in the ethanolic extract that have a high affinity for the RECQL5 protein.

Fig. 7

Interactions between RECQL5 protein and campesterol (A), benzo[H]quinoline, 2,4-dimethyl- (B), vitamin E (C), γ-sitosterol (D), and stigmasterol (E).

Fig. 8

Heatmap indicating chromosomal aberrations and mitotic indices observed in Allium cepa treated with sodium azide (NaN₃) and ethanolic extract of Cyperus esculentus (EECE). Values with different superscripts (a-c) across row indicate statistically different result at P<0.05. NC, negative control (distilled water); PC, positive control (250 μg/L NaN₃); PR, pre-treatment with 200 mg/kg EECE after initial exposure to 250 μg/L NaN₃; PO1, post-treatment with 100 mg/kg EECE after initial exposure to 250 μg/L NaN₃; PO2, post-treatment with 200 mg/kg EECE after initial exposure to 250 μg/L NaN₃; SE, standard error; MN, micro nucleus; AB, anaphasic bridge; MA, multipolar anaphase; NB, nucleus bud; BM, chromosomal break in metaphase; BA, chromosomal break in anaphase; BT, chromosomal break in telophase; CBM, chromosomal bridge in metaphase; CBA, chromosomal bridge in anaphase; CBT, chromosomal bridge in telophase; CA, chromosomal aberrations; TFA, total frequency of aberrations; MI, mitotic index; DR, damage reduction.