Evaluation of Antioxidant and Antibacterial Activities, Cytotoxicity of Acacia seyal Del Bark Extracts and Isolated Compounds.

Abdirahman Elmi,Rosella Spina,Ali Mérito,Arnaud Risler,Fatouma Mohamed Abdoul-Latif,Dominique Laurain-Mattar,Raphaël E Duval,Stéphanie Philippot

doi:10.3390/molecules25102392

Abstract

Water extract of Acacia seyal bark is used traditionally by the population in Djibouti for its anti-infectious activity. The evaluation of in vitro antibacterial, antioxidant activities and cytotoxicity as well as chemical characterization of Acacia seyal bark water and methanolic extracts were presented. The water extract has a toxicity against the MRC-5 cells at 256 μg/mL while the methanolic extract has a weak toxicity at the same concentration. The methanolic extract has a strong antioxidant activity with half maximal inhibitory concentration (IC50) of 150 ± 2.2 μg/mL using 1-diphenyl-2-picrylhydrazyl (DPPH) and IC50 of 27 ± 1.3 μg/mL using 2,2′-azino-bis 3-ethylbenzthiazoline-6-sulphonic acid (ABTS) radical methods. For ferric reducing/antioxidant power (FRAP) assay, the result is 45.74 ± 5.96 μg Vitamin C Equivalent (VCE)/g of dry weight (DW). The precipitation of tannins from methanol crude extract decreases the MIC from 64 µg/mL to 32 µg/mL against Staphylococcus aureus and Corynebacterium urealyticum. However, the antioxidant activity is higher before tannins precipitation than after (IC50 = 150 µg/mL for methanolic crude extract and 250 µg/mL after tannins precipitation determined by DPPH method). By matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) analysis, the results showed that the condensed tannins consist of two types of catechin and gallocatechin-based oligomers. The fractionation led to the identification of three pure compounds: two flavanols catechin and epicatechin; one triterpene as lupeol; and a mixture of three steroids and one fatty acid: campesterol, stigmasterol, clionasterol, and oleamide.

Highlights

The genus Acacia, belonging to the Fabaceae family, is composed of more than 1350 species of trees and shrubs found mostly in semi-arid places in Australia and Africa
The total polyphenolic contents were expressed as mg gallic acid equivalent (GAE)/g of dry materials and the total flavonoid contents were expressed as mg quercetin equivalent (QE)/g of dry materials
The results obtained suggest that A. seyal bark could be a potential source of active natural compounds like flavonoids, steroids, triterpenes, and tannins as catechin and gallocatechin-based oligomers

Summary

Introduction

The genus Acacia, belonging to the Fabaceae family, is composed of more than 1350 species of trees and shrubs found mostly in semi-arid places in Australia and Africa. Acacia is known because of its production of Arabic gum [2] such as Acacia nilotica. This plant is popular for its medicinal use and for scientific interest to search bioactive constituents. The phytochemistry of the genus Acacia differs according to the species and is not known very precisely. Several families of active chemical compounds are found in the literature such as tannins, flavonoids, alkaloids, terpenes, fatty acids, polysaccharides, anthocyanins, and saponins from different parts of Acacia [3,4,5,6]. The bark of various species of Acacia is traditionally used to treat

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