Identification of tissues responsible for the conjugative metabolism of liquiritigenin in rats: an analysis based on metabolite kinetics

Biotransformation of Liquiritigenin into Characteristic Metabolites by the Gut Microbiota

The bioavailability of flavonoids is generally low after oral administration. The metabolic transformation of flavonoids by the gut microbiota may be one of the main reasons for this, although these metabolites have potential pharmacological activities. Liquiritigenin is an important dihydroflavonoid compound found in Glycyrrhiza uralensis that has a wide range of pharmacological properties, such as antitumor, antiulcer, anti-inflammatory, and anti-AIDS effects, but its mechanism of action remains unclear. This study explored the metabolites of liquiritigenin by examining gut microbiota metabolism and hepatic metabolism in vitro. Using LC-MS/MS and LC/MSⁿ-IT-TOF techniques, three possible metabolites of liquiritigenin metabolized by the gut microbiota were identified: phloretic acid (M3), resorcinol (M4), and M5. M5 is speculated to be davidigenin, which has antitumor activity. By comparing these two metabolic pathways of liquiritigenin (the gut microbiota and liver microsomes), this study revealed that there are three main metabolites of liquiritigenin generated by intestinal bacteria, which provides a theoretical basis for the study of pharmacologically active substances in vivo.

Sulfation disposition of liquiritigenin in SULT1A3 overexpressing HEK293 cells: The role of breast cancer resistance protein (BCRP) and multidrug resistance-associated protein 4 (MRP4) in sulfate efflux of liquiritigenin

This study aimed to investigate the cellular disposition of liquiritigenin via the sulfonation pathway and the role of efflux transporters in liquiritigenin sulfate excretion. The sulfonation disposition of liquiritigenin was investigated using SULT1A3 overexpressed HEK293 cells (HEK-SULT1A3 cells). Liquiritigenin generated one mono-sulfate metabolite (7-O-sulfate) in HEK-SULT1A3 cell lysate. And the sulfonation followed the Michaelis-Menten kinetic (V_max = 0.84 nmol/min/mg and K_m = 7.12 μM). Expectedly, recombinant SULT1A3 (hSULT1A3) showed a highly similar kinetic profile with cell lysate. Furthermore, 7-O-sulfate was rapidly generated and excreted in HEK-SULT1A3 cells. Ko143 (a BCRP-selective inhibitor) at 20 μM significantly decreased the excretion rate of liquiritigenin sulfate (>42.5%, p < 0.001). Moreover, the pan-MRPs inhibitor MK-571 at 20 μM essentially abolished the liquiritigenin sulfate effluxion, resulting in the marked reduction of excretion rate (>97.4%, p < 0.001). Furthermore, knockdown of BCRP led to moderate reduction in sulfate excretion (15.9%-16.9%, p < 0.05). Silencing of MRP4 caused significant decreased in sulfate excretion (20.2%-32.5%, p < 0.01). In conclusion, one sulfate metabolite was generated from liquiritigenin in HEK-SULT1A3 cells. BCRP and MRP4 should be the key factors for the cellular excretion of liquiritigenin sulfate.

A targeted strategy to identify untargeted metabolites from in vitro to in vivo: Rapid and sensitive metabolites profiling of licorice in rats using ultra-high performance liquid chromatography coupled with triple quadrupole-linear ion trap mass spectrometry

It is challenging to conduct in vivo metabolic study for traditional Chinese medicines (TCMs) because of complex components, unpredictable metabolic pathways and low metabolite concentrations. Herein, we proposed a sensitive strategy to characterize TCM metabolites in vivo at an orally clinical dose using ultra-high performance liquid chromatography-triple quadrupole-linear ion trap mass spectrometry (UHPLC-QTRAP-MS). Firstly, the metabolism of individual compounds in rat liver microsomes was studied to obtain the metabolic pathways and fragmentation patterns. The untargeted metabolites in vitro were detected by multiple ion monitoring-enhanced product ion (EPI) and neutral loss-EPI scans. Subsequently, a sensitive multiple reaction monitoring-EPI method was developed according to the in vitro results and predicted metabolites to profile the in vivo metabolites. Licorice as a model herb was used to evaluate and validate our strategy. A clinical dose of licorice water extract was orally administered to rats, then a total of 45 metabolites in urine, 21 metabolites in feces and 35 metabolites in plasma were detected. Among them, 18 minor metabolites have not been reported previously and 6 minor metabolites were first detected in vivo. Several isomeric metabolites were well separated and differentiated in our strategy. These results suggested that this new strategy could be widely used for the detection and characterization of in vivo metabolites of TCMs.

Stereospecific pharmacokinetic characterization of liquiritigenin in the rat

Liquiritigenin is a chiral flavonoid present in licorice and other medicinal plants. The nature of its biological fate with respect to the individual enantiomers has not been examined. In this study, we characterize, for the first time, the stereoselective pharmacokinetics of liquiritigenin. Liquiritigenin was intravenously (20 mg/kg) and orally (50 mg/kg) administered to male Sprague-Dawley rats (n = 4 per route of administration). Concentrations in serum and urine were characterized via stereospecific reversed-phase, isocratic HPLC method with UV detection. Serum concentrations were quantified but rapidly fell to undetectable levels. S-liquiritigenin showed a short half-life (0.25-0.54 h), while a better estimation of half-life (26-77 h) and other pharmacokinetic parameters was observed using urinary data. The flavonoid is predominantly excreted via non-renal routes (f_e values of 0.16-3.46 %), and undergoes rapid and extensive phase II metabolism. Chiral differences in the chemical structure of the compound result in some pharmacokinetic differences. Serum concentrations rapidly declined, making modeling difficult. S-liquiritigenin showed an increased urinary half-life.

Identification of metabolites of Si-Ni-San, a traditional Chinese medicine formula, in rat plasma and urine using liquid chromatography/diode array detection/triple-quadrupole spectrometry

Si-Ni-San (SNS) is a widely used traditional Chinese medicine formula (TCMF) in treating various diseases. However, the in vivo integrated metabolism of its multiple components remains unknown. In this paper, a liquid chromatography coupled with diode array detection and triple-quadrupole spectrometry (LC-DAD-MS/MS) method was developed for detection and identification of SNS metabolites in rat plasma and urine at a normal clinical dosage. Accurate structural elucidation was performed using MS/MS, UV data and n-octanol/water partition coefficient. Based on the proposed strategy, 36 absorbed compounds and 29 metabolites in plasma and 33 metabolites in urine were detected by a highly sensitive MRM method. Our results indicated that phase II reactions (e.g., methylation, glucuronidation and sulfation) were the main metabolic pathways of gallic acid and flavanones, while phase I reactions (e.g., hydroxylation) were the major metabolic reaction for triterpenoid saponins. The metabolite profile analysis of SNS provided a comprehensive understanding of the in vivo metabolic fates of constituents in SNS. Moreover, the results in this work demonstrated the present strategy based on the combination of chromatographic, spectrophotometric, mass-spectrometric, and software prediction to detect and identify metabolites was effective and reliable. And such a strategy may also be extended to investigate the metabolism of other TCMF.

Effects of acute renal failure induced by uranyl nitrate on the pharmacokinetics of liquiritigenin and its two glucuronides, M1 and M2, in rats

OBJECTIVES

Liver disease and acute renal failure (ARF) are closely associated. The pharmacokinetics of liquiritigenin (LQ), a candidate therapy for inflammatory liver disease, and its metabolites M1 and M2 were evaluated in rats with ARF induced by uranyl nitrate (U-ARF rats).

METHODS

LQ was administered intravenously (20 mg/kg) or orally (50 mg/kg) in U-ARF and control rats, and uridine diphosphate-glucuronosyltransferases (UGT) activity and uridine 5'-diphosphoglucuronic acid (UDPGA) concentrations were determined in the liver and intestine.

KEY FINDINGS

After intravenous LQ administration, U-ARF rats displayed significantly slower LQ renal clearance but no significant changes in the LQ area under the plasma concentration-time curve (AUC) compared with controls. This was because of similar hepatic UGT activity and UDPGA levels between two groups, which resulted in comparable non-renal clearance, as well as the limited contribution of LQ renal clearance to total LQ clearance. However, the AUC and AUC(M) /AUC(LQ) ratios of M1 and M2 were significantly increased in U-ARF rats because of decreased urinary excretion of M1 and M2. Similar results were observed following oral administration because of the comparable LQ intestinal metabolism in both groups and decreased urinary excretion of M1 and M2 in U-ARF rats.

CONCLUSIONS

U-ARF rats displayed decreased urinary excretion of LQ glucuronides, resulting in significantly greater AUC and metabolite ratios of M1 and M2 following LQ administration.

Liquiritigenin pharmacokinetics in a rat model of diabetes mellitus induced by streptozotocin: greater formation of glucuronides in the liver, especially M2, due to increased hepatic uridine 5'-diphosphoglucuronic acid level

Liquiritigenin (LQ) is a candidate for the treatment of inflammatory liver disease. Many studies have confirmed that hepatic disease and diabetes mellitus are closely associated. Thus, the pharmacokinetic changes of LQ and its 2 glucuronides, M1 and M2, in a rat model of diabetes mellitus induced by streptozotocin (DMIS rats) were evaluated. Liquiritigenin was administered intravenously (20 mg/kg) or orally (50 mg/kg) in DMIS and control rats. Changes in in vitro activity and in vivo uridine 5'-diphosphoglucuronic acid level in the liver and intestine of DMIS rats compared with controls were also studied. After intravenous administration of LQ in DMIS rats, no significant changes in the pharmacokinetic parameters of LQ were observed. However, the AUC(M2)/AUC(LQ) ratio was significantly greater (by 53.0%) than that of controls. After oral administration of LQ, the AUC of LQ and metabolite ratios of M1 and M2 were comparable to controls. The increase in the formation of glucuronides of LQ, especially M2, after intravenous administration of LQ was due to the increased in vivo hepatic uridine 5'-diphosphoglucuronic acid level in DMIS rats as a result of alteration in carbohydrate metabolism in diabetes. The comparable pharmacokinetics of LQ, M1, and M2 after oral administration of LQ were mainly due to the comparable intestinal metabolism of LQ between the control and DMIS rats.

Liquiritigenin, a flavonoid aglycone from licorice, has a choleretic effect and the ability to induce hepatic transporters and phase-II enzymes

Liquiritigenin (LQ), an active component of licorice, has an inhibitory effect on LPS-induced inhibitory nitric oxide synthase expression. This study investigated the effects of LQ on choleresis, the expression of hepatic transporters and phase-II enzymes, and fulminant hepatitis. The choleretic effect and the pharmacokinetics of LQ and its glucuronides were monitored in rats. After intravenous administration of LQ, the total area under the plasma concentration-time curve of glucuronyl metabolites was greater than that of LQ in plasma, which accompanied elevations in bile flow rate and biliary excretion of bile acid, glutathione, and bilirubin. The expressions of hepatocellular transporters and phase-II enzymes were assessed by immunoblots, real-time PCR, and immunohistochemistry. In the livers of rats treated with LQ, the protein and mRNA levels of multidrug resistance protein 2 and bile salt export pump were increased in the liver, which was verified by their increased localizations in canalicular membrane. In addition, LQ treatment enhanced the expression levels of major hepatic phase-II enzymes. Consistent with these results, LQ treatments attenuated galactosamine/LPS-induced hepatitis in rats, as supported by decreases in the plasma alanine aminotransferase, liver necrosis, and plasma TNF-alpha. These results demonstrate that LQ has a choleretic effect and the ability to induce transporters and phase-II enzymes in the liver, which may be associated with a hepatoprotective effect against galactosamine/LPS. Our findings may provide insight into understanding the action of LQ and its therapeutic use for liver disease.

Oxidative in vitro metabolism of liquiritigenin, a bioactive compound isolated from the Chinese herbal selective estrogen beta-receptor agonist MF101

Liquiritigenin [2,3-dihydro-7-hydroxy-2-(4-hydroxyphenyl)-(S)-4H-1-benzopyran-4-one] is one of the major active compounds of MF101, an herbal extract currently in clinical trials for the treatment of hot flashes and night sweats in postmenopausal women. MF101 is a selective estrogen receptor beta agonist but does not activate the estrogen receptor alpha. Incubation with pooled human liver microsomes yielded a single metabolite. Its structure was elucidated using tandem mass spectrometry in combination with analysis of the fragmentation patterns. The metabolite resulted from the loss of two hydrogens and rearrangement to the stable 7,4'-dihydroxyflavone. The structure was also confirmed by comparison with authentic standard material. Maximum apparent reaction velocity (V(max)) and Michaelis-Menten constant (K(m)) for the formation of 7,4'-dihydroxyflavone were 32.5 nmol/g protein/min and 128 microM, respectively. After correction for protein binding (free fraction = 0.84), the apparent intrinsic clearance (CL(int)) for 7,4'-dihydroxyflavone formation was 0.3 ml/g/min. Liquiritigenin was almost exclusively metabolized by CYP3A enzymes. Comparison of liquiritigenin metabolism in human liver microsomes isolated from 16 individuals showed 9.5-fold variability in metabolite formation (3.4-32.2 nmol/g protein/min). An estrogen receptor luciferase assay indicated that the metabolite was a 3-fold more potent activator of the estrogen receptor beta than the parent compound and did not activate the estrogen receptor alpha.

Anti-inflammatory effects of liquiritigenin as a consequence of the inhibition of NF-kappaB-dependent iNOS and proinflammatory cytokines production

BACKGROUND AND PURPOSE

Glycyrrhizae radix has been widely used as a cytoprotective, plant-derived medicine. We have identified a flavanoid, liquiritigenin, as an active component in extracts of Glycyrrhizae radix. This research investigated the effects of liquiritigenin on the induction of inducible NOS (iNOS) and proinflammatory cytokines by lipopolysaccharide (LPS) in Raw264.7 cells, and on paw oedema in rats.

EXPERIMENTAL APPROACH

iNOS expression was determined by western blotting, real-time reverse transcription-PCR and reporter gene analyses. Tumour necrosis factor-alpha (TNF-alpha), interleukin (IL)-1beta and IL-6 were assayed by ELISA. Gel shift assay and immunoblotting were used to assess NF-kappaB activation. The effect of liquiritigenin on acute inflammation in vivo was evaluated using carrageenan-induced paw oedema.

KEY RESULTS

Treatment of Raw264.7 cells with liquiritigenin caused inhibition of LPS-induced NF-kappaB DNA binding activity, due to repression of I-kappaBalpha phosphorylation and degradation. Liquiritigenin treatment prevented LPS from increasing the levels of iNOS protein and mRNA in a concentration-dependent manner. Liquiritigenin also suppressed the production of TNF-alpha, IL-1beta and IL-6 from Raw264.7 cells after LPS. In rats, liquiritigenin treatment inhibited formation of paw oedema induced by carrageenan.

CONCLUSION AND IMPLICATIONS

These results demonstrate that liquiritigenin exerts anti-inflammatory effects, which results from the inhibition of NF-kappaB activation in macrophages, thereby decreasing production of iNOS and proinflammatory cytokines. Our findings showing inhibition by liquiritigenin of paw oedema as well as inflammatory gene induction will help to understand the pharmacology and mode of action of liquiritigenin, and of the anti-inflammatory use of Glycyrrhizae radix.

Glucuronidation versus oxidation of the flavonoid galangin by human liver microsomes and hepatocytes

In a previous study, we used human liver microsomes for the first time to study cytochrome P450 (P450)-mediated oxidation of the flavonoid galangin. The combination of CYP1A2 and CYP2C9 produced a V(max)/K(m) value of 13.6 +/- 1.1 microl/min/mg of protein. In the present extended study, we determined glucuronidation rates for galangin with the same microsomes. Two major and one minor glucuronide were identified by liquid chromatography/mass spectrometry. The V(max)/K(m) values for the two major glucuronides conjugated in the 7- and 3-positions were 155 +/- 30 and 427 +/- 26 microl/min/mg of protein, thus, exceeding that of oxidation by 11 and 31 times, respectively. This highly efficient glucuronidation appeared to be catalyzed mainly by the UDP-glucuronosyltransferase (UGT)1A9 isoform but also by UGT1A1 and UGT2B15. Sulfation of galangin by the human liver cytosol, mediated mainly but not exclusively by sulfotransferase (SULT) 1A1, also appeared to be efficient. These conclusions were strongly supported by experiments using the S9 fraction of the human liver, in which all three metabolic pathways could be directly compared. When galangin metabolism was examined in fresh plated hepatocytes from six donors, glucuronidation clearly predominated followed by sulfation. Oxidation occurred only to a minor extent in two of the donors. This study for the first time establishes that glucuronidation and sulfation of galangin, and maybe other flavonoids, are more efficient than P450-mediated oxidation, clearly being the metabolic pathways of choice in intact cells and therefore likely also in vivo.

The herbal medicine Shosaiko-to exerts different modulating effects on lung local immune responses among mouse strains

Shosaiko-to (SST), a Chinese/Japanese traditional herbal medicine, has recently been demonstrated to increase lung interleukin-6 (IL-6) levels and to ameliorate pulmonary disorders in BALB/c mice (BALB). In the present study, we examined the effects of SST on lung cytokine levels and lipopolysaccharide (LPS)-induced lung injury in C57BL/6 mice (B6), which are known to show different immune responses from BALB due to the difference in genetic backgrounds. In B6, in contrast with BALB, SST decreased lung IL-6 levels and exacerbated LPS-induced lung injury. Investigation of the active components of SST suggested that multiple ingredients were supposed to be responsible for IL-6-attenuating activity in vivo. Further, we examined the effect of metabolites of major ingredients of SST on IL-6 production from lung immune cells in vitro. Saikogenin D and oroxylin A attenuated IL-6 production in LPS-stimulated alveolar macrophages of B6 more than in that of BALB. Liquiritigenin, which was previously reported to enhance IL-6 production in anti-CD3 monoclonal antibody-stimulated lung mononuclear cells of BALB, showed no effect on that of B6. These findings suggest that SST may have different, possibly even opposite, effects on lung immunity in hosts with different genetic backgrounds.

Up-regulation of carnitine transporters helps maintain tissue carnitine levels in carnitine deficiency induced by pivalic acid

PURPOSE

Pivalic acid (PVA) forms conjugates with endogenous carnitine and enhances its excretion. The purpose of this study is to determine whether tissue carnitine levels decrease in parallel with plasma levels in carnitine deficiency induced by PVA.

METHODS

PVA was orally administered to rats for 5 days. Carnitine levels in plasma, liver, kidney, muscle, and heart were monitored. The tissue uptake clearance (CLuptake) was determined in vivo by the integration plot method. Hepatocytes were prepared from control and PVA-treated rats, and the uptake of L-carnitine was determined.

RESULTS

Plasma concentrations of L-carnitine decreased as a result of the enhanced carnitine elimination as pivaloylcarnitine (PCN) when rats were treated with PVA. However, L-carnitine concentrations in liver, muscle, and heart remained relatively constant during the study. period. CLuptake increased in liver and muscle and, thus, the rate of carnitine uptake from plasma into these tissues did not change even at low plasma concentrations. This helps maintain carnitine levels in these tissues. Up-regulation of carnitine transporters is suggested to be a mechanism for the increased CLuptake.

CONCLUSIONS

In the carnitine deficiency state induced by PVA, increased CLuptake owing to up-regulation of carnitine transporters is suggested to help maintain carnitine levels in some tissues.

Modulation of lung local immune responses by oral administration of a herbal medicine Sho-saiko-to

Sho-saiko-to (SST), a Chinese/Japanese herbal medicine (Kampo medicine) widely used to treat chronic hepatitis in Japan, is known to modulate immune responses, and thus its immunomodulating activity may be responsible for its bi-directional effects on the lungs as therapeutic efficacy in various lung diseases and involvement in development of interstitial pneumonia. We administered SST to BALB/c mice orally and examined the lung tissue levels of pro/anti-inflammatory cytokines, interleukin-1beta (IL-1beta), tumor necrosis factor-alpha (TNF-alpha) and interleukin-6 (IL-6), and the effects of SST on acute lung injury induced by instillation of lipopolysaccharide (LPS) or IL-1. Although SST had no effect on lung TNF-alpha or IL-1beta level, it increased IL-6. Investigation of active fractions of SST suggested that multiple ingredients were supposed to be responsible for IL-6-inducing activity. Liquiritigenin, a metabolite of liquiritin which is one of the major ingredients in SST enhanced in vitro IL-6 production in anti-CD3 monoclonal antibody (anti-CD3 mAb)-stimulated lung mononuclear cells in a cell-type specific and dose-dependent manner. SST suppressed LPS-induced lung injury at the later phase when lung leak was evident while being ineffective on initial neutrophil sequestration to the lung in these models. These findings suggest that SST modulates lung inflammation by regulating local immune response.

Biliary excretion of glycyrrhizin in rats: kinetic basis for multiplicity in bile canalicular transport of organic anions

PURPOSE

To examine the presence of multiplicity for the biliary excretion of xenobiotic conjugates, we studied the disposition of glycyrrhizin (GR), which has glucuronide within its molecular structure and has the ability to inhibit the biliary excretion of liquiritigenin (LG) glucuronides.

METHODS

GR was administered intravenously as a bolus to Sprague-Dawley (SD) rats which received an i.v. infusion of inhibitors (dibromosulfophthalein (DBSP) and indocyanine green (ICG)) at their transport maximum rates. Biliary excretion of GR was also examined in Eisai hyperbilirubinemic rats (EHBR), which have a hereditary defect in the canalicular transport system of several organic anions.

RESULTS

Infusion of ICG did not affect the biliary excretion of GR, whereas infusion of DBSP reduced it significantly. The plasma concentration of GR was increased by DBSP but not by ICG. In EHBR, the biliary excretion of GR was severely impaired, resulting in an increase in the plasma concentration of GR.

CONCLUSIONS

These findings suggest (1) that the biliary excretion of GR is mediated by the system which is shared by DBSP and LG glucuronides but not by ICG and (2) that this system is hereditarily defective in EHBR. Together with our previous findings, the multiplicity for the biliary excretion of organic anions is shown.