Inhibition of IL-6 and IL-8 production in LPS-stimulated human gingival fibroblasts by glycyrrhizin via activating LXRα.

The aim of this study was to clarify the anti-inflammatory effects and its molecular mechanism of glycyrrhizin on LPS-stimulated human gingival fibroblasts (HGFs), which will be of benefit for periodontitis treatment. An MTT assay was performed to assess the effects of glycyrrhizin on cellular viability. The levels of IL-6 and IL-8 were measured by ELISA. The expression of iNOS, COX-2, NF-κB, and LXRα were detected by western blot analysis. The results showed that glycyrrhizin significantly inhibited LPS-induced IL-6 and IL-8 production, as well as COX-2 and iNOS expression. LPS-induced NF-κB activation in HGFs was also inhibited by treatment of glycyrrhizin. Furthermore, glycyrrhizin increased the expression of LXRα in a concentration-dependent manner. In addition, the inhibition of glycyrrhizin on IL-6 and IL-8 production was reversed by LXRα inhibitor GGPP. In conclusion, these results indicated that glycyrrhizin exhibited its anti-inflammatory effects in HGFs by activating LXRα.

Analysis of the synergistic effect of glycyrrhizin and other constituents in licorice extract on lipopolysaccharide-induced nitric oxide production using knock-out extract.

The pharmacological evidence for synergism between natural compounds is not fully elucidated. In this study, we investigated the synergistic function of one target compound in medicinal plant extract by using knock-out (KO) extract, which is one target compound-eliminated extract from whole crude extract. Licorice is the most important ingredient used in the traditional Chinese medicine (TCM) and the Japanese Kampo medicine, and one of the major active components of licorice is glycyrrhizin (GC). To identify the potential role of GC, we prepared GC-removed extract (GC-KO extract) from licorice extract (LE) using immunoaffinity column conjugated with anti-GC monoclonal antibody (MAb), which could eliminate 99.5% of GC from LE. LE inhibited nitric oxide (NO) production and inducible NO synthase (iNOS) expression in lipopolysaccharide (LPS)-stimulated RAW264 murine macrophage cells. However, treatment of GC alone could not show the suppression of NO production and iNOS expression. Interestingly, the inhibitory effect of GC-KO extract was significantly attenuated compared with LE. Furthermore, the combined treatment with GC-KO extract and GC could improve the attenuated inhibition. Taken together, our results indicate that GC may exert synergistic suppression of iNOS expression when coexisting with the other constituents contained in LE, and KO extract is a useful approach for determination of real pharmacological functions of natural compound in the phytochemical mixture.

Effects of glucose, fructose and 5-hydroxymethyl-2-furaldehyde on the presystemic metabolism and absorption of glycyrrhizin in rabbits.

Our previous study reported that co-administration of honey significantly increased the serum levels of glycyrrhetic acid (GA) after oral administration of glycyrrhizin (GZ) in rabbits. The components of honey are sucrose, glucose, fructose and 5-hydroxymethyl-furaldehyde (HMF). To clarify the causative component(s) in honey that altered the metabolic pharmacokinetics of GZ, rabbits were given GZ (150 mg kg(-1)) with and without glucose (5 g/rabbit), fructose (5 g/rabbit) and HMF (1 mg kg(-1)), respectively, in crossover designs. An HPLC method was used to determine concentrations of GZ and GA in serum as well as GA and 3-dehydroglycyrrhetic acid (3-dehydroGA) in faeces suspension. A noncompartment model was used to calculate the pharmacokinetic parameters and analysis of variance was used for statistical comparison. Our results indicated that the area under curve (AUC) of GA was significantly increased by 29% when HMF was coadministered, whereas the pharmacokinetics of GZ and GA were not significantly altered by coadministration of glucose or fructose. An in-vitro study, using faeces to incubate GZ and GA individually, indicated that HMF significantly inhibited the oxidation of GA to 3-dehydroGA and this may explain the enhanced GA absorption in-vivo. It was concluded that HMF is the causative component in honey that affects the presystemic metabolism and pharmacokinetics of GZ in-vivo.