Rapid and Sensitive Liquid Chromatography-Tandem Mass Spectrometry for Quantification of Glycyrrhetic Acid in Human Plasma

A simple, rapid and sensitive liquid chromatography-tandem mass spectrometry（LC-MS/MS） for the determination of glycyrrhetic acid in human plasma with ginsenoside Rh2 as internal standard was developed and validated. The plasma samples were prepared via liquid-liquid extraction with ethyl acetate. Chromatographic separation was accomplished on a Venusil MP-C18（50 mm×2.1 mm, 5 μm i.d.） column at 25 °C. The mobile phase consisted of acetonitrile/5 mmol？L-1 ammonium acetate（10：90, volume ratio） at a flow rate of 0.4 mL/min. Negative electrospray ionization was utilized as the ionization source. Glycyrrhetic acid and internal standard were determined via the mutiple reaction monitoring of precursor→production ion transitions at m/z 469→425, 409 and m/z 621→161, respectively. Each sample was chromatographed within 2.5 min. The lower limit of quantification was 0.50 ng/mL for 200 μL of plasma sample and the linear range was from 0.50 ng/mL to 800 ng/mL. The intra- and inter-day precisions were less than 8.76% in terms of relative standard deviation（RSD）, and the accuracy was within a range of -3.25%-1.32% in terms of relative error（RE）. The method was successfully applied to the pharmacokinetic studies of glycyrrhetic acid in healthy male Chinese volunteers after a single oral administration of 75 mg of glycyrrhizin.

In vitro Metabolism of Strychnine by Human Cytochrome P450 and Its Interaction with Glycyrrhetic Acid

Objective To investigate the metabolism of strychnine(STN)and the metabolic interaction between STN and glycyrrhetic acid(GA)in vitro.Methods Human liver microsomes(HLM)and human recombinant cytochrome P450(CYP)isoforms were employed to study the metabolism of STN and the metabolic interaction of STN with GA in vitro.Results In HLM,the Km,Vmax,and clearance of STN were 88.50μmol/L,0.88 nmol/(mg·min),and 9.93 mL/(mg·min),respectively.STN was metabolized mainly by CYP3A4.However,STN noncompetitively inhibited CYP3A4-catalyzed testosterone 6β-hydroxylation with IC50 value of 5.9μmol/L and Ki value of 5.5 μmol/L.Moreover,GA competitively inhibited STN metabolism with IC50 value of 10.6μmol/L and Ki value of 17.7μmol/L.Conclusion Although STN is mainly metabolized by CYP3A4 in vitro,STN has noncompetitive inhibition on CYP3A4-catalyzed testosterone 6β-hydroxylation.Moreover,GA could competitively inhibit STN metabolism.The present work is helpful to elucidate the metabolic interaction between STN and GA.

O-glycosyltransferases from Homo sapiens contributes to the biosynthesis of Glycyrrhetic Acid 3-O-mono-β-D-glucuronide and Glycyrrhizin in Saccharomyces cerevisiae

Glycyrrhizin(GL)and Glycyrrhetic Acid 3-O-mono-β-D-glucuronide(GAMG)are the typical triterpenoid glycosides found in the root of licorice,a popular medicinal plant that exhibits diverse physiological effects and pharmacological manifestations.However,only few reports are available on the glycosylation enzymes involved in the biosynthesis of these valuable compounds with low conversion yield so far.In mammals,glycosyltransferases are involved in the phase II metabolism and may provide new solutions for us to engineer microbial strains to produce high valued compounds due to the substrate promiscuity of these glycosyltransferases.In this study,we mined the genomic databases of mammals and evaluated 22 candidate genes of O-glycosyltransferases by analyzing their catalytic potential for O-glycosylation of the native substrate,glycyrrhetinic acid(GA)for its glycodiversification.Out of 22 selected glycosyltransferases,only UGT1A1 exhibited high catalytic performance for biosynthesis of the key licorice compounds GL and GAMG.Molecular docking results proposed that the enzymatic activity of UGT1A1 was likely owing to the stable hydrogen bonding interactions and favorite conformations between the amino acid residues around substrate channels(P82~R85)and substrates.Furthermore,the complete biosynthesis pathway of GL was reconstructed in Saccharomyces cerevisiae for the first time,resulting in the production of 5.98±0.47 mg/L and 2.31±0.21 mg/L of GL and GAMG,respectively.

Study of binding glycyrrhetic acid to AT_1 receptor

To analyze the binding of glycyrrhetic acid (GA) to angiotensin II type I (AT1) receptor and to explore the mechanisms underlying the binding, primary cell culture of rat vascular smooth muscle cell (VSMC), radioactive ligand-receptor binding assay, lascer confocal scanning micro-scope (LCSM), Northern blot, 3H-TdR incorporation DNA assay were used in this study. The re-sults suggest that specific binding of GA to AT1 receptor (IC50 value was 35.0 mmol/L) increases intracellular [Ca2+]i of VSMC, activates transcription factor c-myc and promotes the proliferation of VSMC, therefore GA was probably an agonist of AT1 receptor, providing a new target for GA抯 pharmaceutical effects.

Pharmacological Modulation by Shakuyakukanzoto (Shao-Yao-Gan-Cao-Tang) and the Ingredients in Rat Intestinal Smooth Muscle

Shakuyakukanzoto (Shao-Yao-Gan-Cao-Tang), a formulation of Japanese herbal (Kampo) medicines, is composed of Paeoniae Radix and Glycyrrhizae Radix. Effects of Shakuyakukanzoto and the ingredients on rat intestinal tract were examined. Shakuyakukanzoto (0.01 - 0.3 mg/ml) relaxed a carbachol (CCh, 0.3 μM) - induced contraction in a concentration-dependent manner. Both components (Paeoniae radix and Glycyrrhizae radix) also relaxed the CCh-induced contraction. At 0.1 to 1 mM, their constituents (paeoniflorin and glycyrrhetic acid) and the metabolic products (18-α- and 18-β-glycyrrhetinic acids) exerted almost the same actions. The relaxations induced by Shakuyakukanzoto were not modified by 1 μM nicardipine, 10 μM suramin (ATP receptor inhibitor) and several K+ channel inhibitors, but was attenuated by 20 μM IBMX (a phosphodiesterase inhibitor). Also, IBMX inhibited the relaxations induced by paeoniflorin and glycyrrhetic acid, but not by other ingredients. Nicardipine decreased the relaxation of just 18-α-glycyrrhetinic acid. Even in non-treatment with CCh, Shakuyakukanzoto relaxed the intestinal tract. CCh (0.3 μM) elicited spontaneous contractions in 23% specimens, depressed by application of Shakuyakukanzoto. These results indicate that Shakuyakukanzoto causes a remarkable relaxation by the anti-cholinergic and the PDE inhibitory actions, but by minor contribution of Ca2+ channel inhibition. Thus, Shakuyakukanzoto exerts an anti-spasmodic action due to the interaction with pharmacological effects of its ingredients.

Development of a validated UPLC-qTOF-MS/MS method for determination of bioactive constituent from Glycyrrhiza glabra

An ultra-performance liquid chromatography quadrupole time of flight mass spectrometry （UPLC-qTOF-MS/MS） method was developed and validated for the simultaneous determination of glycyrrhizin and glycyrrhetic acid. These analytes were separated on a reverse phase C18 column using a mobile phase of acetonitrile：2% acetic acid in water （75：25, v/v） with a flow rate of 200 μL/min. The qTOF-MS was operated under multiple reaction monitoring （MRM） mode using the electrospray ionization （ESI） technique with positive ion polarity. A comparison of three different extraction techniques i.e. accelerated solvent extraction （ASE）, extraction under ultrasonic waves （USW） and the classical extraction by percolation （CE） method was done and quantification of these extracts was also carried out by the proposed method.

Enhanced production of β-glucuronidase from Penicillium purpurogenum Li-3 by optimizing fermentation and downstream processes

β-Glucuronidase from Penicillium purpuro- genum Li-3 （PGUS） can efficiently hydrolyze glycyrrhizin into the more valuable glycyrrhetic acid monoglucuronide. However, a low productivity of PGUS and the lack of an effective separation strategy have significantly limited its industrial applications. Therefore, the production of PGUS has been improved by optimizing both the fermentation and purification strategies. A two-stage fermentation strategy was developed where PGUS was first grown with glucose and then PGUS was produced in the presence of glycyrrhizin as an inducer. By using this strategy, the biomass was increased 1.5 times and the PGUS activity increased 5.4 times compared to that when glycyrrhizin was used as the sole carbon source. The amount of PGUS produced was increased another 16.6% when the fermentation was expanded to a 15-L fermenter. An effective protocol was also established to purify the PGUS using a sequential combination of hydrophobic, strong anionexchange and gel filtration chromatography. This protocol had a recovery yield of 6% and gave PGUS that was 39 times purer than the crude PGUS. The purified PGUS had a specific activity of 350 U. mg-1.

Effect of strychnine hydrochloride on liver cytochrome P450 mRNA expression and monooxygenase activities in rat

Strychnos nux-vomica L.has been frequently used in traditional Chinese medicine but has high acute toxicity.It is commonly taken with Glycyrrhizae radix to decrease its toxicity but the mechanism of this interaction is unknown.In this work,the mRNA expression and the activity of four cytochrome P450(CYP)enzymes representative of four subfamilies(CYP1A,CYP3A,CYP2C and CYP2E)were determined ex vivo in rat livers from groups of Wistar rats orally administered strychnine hydrochloride(SH)at three doses(0.1,0.3 and 0.9 mg/kg/day)alone and,at the highest dose,in combination with glycyrrhetinic acid(GA,25 mg/kg/day)or liquiritin(LQ,20 mg/kg/day)once a day for 7 consecutive days.Compared to control,the mRNA expressions of CYP3A1,1A2 and 2E1 were higher in rats receiving the highest dose of SH but lower for CYP3A1 and CYP2E1 in rats receiving the SH+GA and SH+LQ combinations.CYP2E1 activity was higher and CYP2C,CYP3A and CYP1A2 activities were lower in rats receiving the highest dose of SH.In contrast CYP1A2 and CYP2C activities were higher and CYP2E1 and CYP3A activities lower in rats receiving the SH+GA combination.CYP2E1 and CYP3A activities were also lower in rats receiving the SH+LQ combination.The results show that treatment with SH for 7 days affects the expression and the activity of CYP enzymes and that coadministration of GA and LQ modulates these effects.This modulation may explain the role of Glycyrrhizae radix in reducing the acute toxicity of Strychnos nux-vomica L.CYPs enzymes.