A pinitol-rich Glycyrrhiza glabra L. leaf extract as functional supplement with potential in the prevention of endothelial dysfunction through improving insulin signalling

Background: Glycyrrhyza glabra L. is one of the most popular medicinal plant in the world, its roots having been used since ancient times in many traditional medicines. On the contrary, scarce attention has been dedicated to liquorice aerial parts. Previous studies showed the presence of a large group of polyphenols and a consistent amount of d-pinitol in the leaf extract.Methods: The methanolic extract from G. glabra leaves was profiled for its content in polyphenols; the amount of d-pinitol was also measured with two independent methods (HPLC-ELSD and NMR). The extract was tested for its in vitro protective effects against insulin resistance-related endothelial dysfunction in human umbilical vein endothelial cells exposed to palmitic acid, which is the most prevalent saturated free fatty acid in circulation.Results: Methanolic extract from liquorice leaves has a protective effect against the lipotoxicity-associated alterations of insulin pathway in human endothelial cells, similarly to what observed with pure d-pinitol.Conclusions: Liquorice leaves are to be considered a waste product which gives a phytocomplex endowed with interesting potential therapeutic properties, moreover the use of a liquorice leaves phytocomplex rather than a pure compound allows avoiding a series of isolation/purification procedures and can be easily scaled up for industrial applications.

Prenylated Phenolic Compounds from the Aerial Parts of Glycyrrhiza uralensis as PTP1B and α-Glucosidase Inhibitors

Glycyrrhiza uralensis (liquorice) is a well-known medicinal plant. Its roots and rhizomes are used as the popular Chinese herbal medicine Gan-Cao. An ethanol extract of the aerial parts of G. uralensis showed antidiabetic effects on db/db mice. It decreased the blood glucose level by 30.3% and increased the serum insulin level by 41.8% compared to the control group. Eighty-six phenolic compounds (1-86) were obtained from the aerial parts, including the new prenylated isoflavanones (1-5), isoflavans (6-9), and a 2-phenylbenzofuran (10). The structures were identified by NMR and HRESIMS data analyses, and the absolute configurations were established by comparing the calculated and experimental ECD spectroscopic data. Compounds 2, 6, and 10 inhibited PTP1B with IC₅₀ values of 5.9, 6.7, and 5.3 μM, respectively. Compound 2 and the known compounds glycycoumarin (76) and glyurallin A (79) inhibited α-glucosidase with IC₅₀ values of 20.1, 0.1, and 0.3 μM, respectively. Compound 4 at 10 μM increased the glucose uptake rate to 95% in an insulin resistance HepG2 cell model (p < 0.01).

Antioxidant and Anti-Inflammatory Activities of Flavanones from Glycyrrhiza glabra L. (licorice) Leaf Phytocomplexes: Identification of Licoflavanone as a Modulator of NF-kB/MAPK Pathway

Inflammation represents an adaptive response generated by injuries or harmful stimuli. Natural remedies represent an interesting alternative to traditional therapies, involving several biochemical pathways. Besides, the valorization of agrochemical wastes nowadays seems to be a feasible way to reduce the health spending and improve the accessibility at bioactive natural compounds. In this context, the chemical composition of three Glycyrrhiza glabra L. (licorice) leaf extracts, obtained through maceration or ultrasound-assisted method (fresh and dried leaves) was investigated. A guided fractionation obtained three main components: pinocembrin, glabranin and licoflavanone. All the extracts showed similar antioxidant properties, evaluated by 2,2′-diphenyl-1-picrylhydrazyl (DPPH) or 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) Diammonium Salt (ABTS) assay, while, among the isolated compounds, licoflavanone exhibited the best antioxidant activity. The anti-inflammatory activity of the extracts and the purified compounds was investigated in lipopolysaccharide (LPS)-stimulated RAW 264.7 murine macrophages. Extract C and licoflavanone showed a good anti-inflammatory activity without affecting cell viability, as they decreased nitrite levels even when used at 12.5 μg/mL (p < 0.005) and 50 μM concentration (p < 0.001), respectively. Interestingly, licoflavanone markedly decreased pro-inflammatory cytokines and cyclooxygenase 2/inducible nitric oxide synthase (COX-2/iNOS) expression levels (p < 0.001). A modulation of nuclear factor kappa B/mitogen-activated protein kinases (NF-kB/MAPK) pathway underlay such behavior, highlighting the potential of this natural compound as a new scaffold in anti-inflammatory drug research.