Unequivocal glycyrrhizin isomer determination and comparative in vitro bioactivities of root extracts in four Glycyrrhiza species - PubMed (original) (raw)

Unequivocal glycyrrhizin isomer determination and comparative in vitro bioactivities of root extracts in four Glycyrrhiza species

Mohamed A Farag et al. J Adv Res. 2015 Jan.

Abstract

Glycyrrhiza glabra, commonly known as licorice, is a popular herbal supplement used for the treatment of chronic inflammatory conditions and as sweetener in the food industry. This species contains a myriad of phytochemicals including the major saponin glycoside glycyrrhizin (G) of Glycyrrhetinic acid (GA) aglycone. In this study, 2D-ROESY NMR technique was successfully applied for distinguishing 18α and 18β glycyrrhetinic acid (GA). ROESY spectra acquired from G. glabra, Glycyrrhiza uralensis and Glycyrrhiza inflata crude extracts revealed the presence of G in its β-form. Anti-inflammatory activity of four Glycyrrhiza species, G, glabra, G. uralensis, G. inflata, and G. echinata roots was assessed against COX-1 inhibition revealing that phenolics rather than glycyrrhizin are biologically active in this assay. G. inflata exhibits a strong cytotoxic effect against PC3 and HT29 cells lines, whereas other species are inactive. This study presents an effective NMR method for G isomer assignment in licorice extracts that does not require any preliminary chromatography or any other purification step.

Keywords: G. glabra; G. inflata; G. uralensis; Glycyrrhizin; Licorice; ROESY.

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Figures

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Graphical abstract

Fig. 1

Fig. 1

Chemical structures of _α_- and _β_-glycyrrhizin. Note the carbon numbering system for each compound is used throughout the manuscript for NMR assignment.

Fig. 2

Fig. 2

Identification of β-glycyrrhizin in _G. uralensi_s crude extract by comparison with the 2D ROESY spectra of α- and β-glycyrrhetic acid. Expansions of 2D ROESY spectra for α-glycyrrhetic acid (A), β-glycyrrhetic acid (B), and G. uralensis extract (C) showing correlations through space between H-18 and CH3-28 in the β-isomers but H-18 and CH3-27 as well as CH3-29 in the α-isomer; arrows point to correlations.

Fig. 3

Fig. 3

Anti-inflammatory activity against COX1 and total phenolics (TP) content of Glycyrrhiza sp. extract tested at a dose of 100 μg ml−1 (n = 3). Results are expressed for anti-inflammatory activity as % inhibition to control on the Y1 axis and for polyphenol content as mg g−1 as displayed on the Y2 axis. Glycyrrhiza samples include: (GE1, GE2, GE3; G. echinata), (GU1, GU2, GU3; G. uralensis), (GG1, GG2, GG3, GG4; G. glabra) and (GI; G. inflata), for sample codes, see Table 1.

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