Regioselective glucuronidation of gingerols by human liver microsomes and expressed UDP-glucuronosyltransferase enzymes: reaction kinetics and activity correlation analyses for UGT1A9 and UGT2B7

Cytochrome P450 metabolism studies of [6]-gingerol, [8]-gingerol, and [10]-gingerol by liver microsomes of humans and different species combined with expressed CYP enzymes

Gingerols, mainly [6]-gingerol (6G), [8]-gingerol (8G), and [10]-gingerol (10G), are the functional and specific pungent phytochemicals in ginger. However, poor oral bioavailability limits their applications owing to extensive metabolism. The present study aims to characterize the cytochrome P450 (CYP) metabolic characteristics of 6G, 8G, and 10G by using pooled human liver microsomes (HLM), different animal liver microsomes, and the expressed CYP enzymes. It is shown that NADPH-dependent oxidation and hydrogenation metabolisms of gingerols are the main metabolic types in HLM. With the increase of the carbon chain, the polarity of gingerols decreases and the formation of hydrogenated metabolites is more efficient (CL_int: 1.41 μL min^-1 mg^-1 for 6G, 7.79 μL min^-1 mg^-1 for 8G and 14.11 μL min^-1 mg^-1 for 10G), indicating that the phase I metabolism of gingerols by HLM varied with the chemical structure of the substrate. The phase I metabolism of gingerols revealed considerable species variations, and compared to HLM, novel metabolites such as (3S,5S)-gingerdiols and demethylated metabolites are generated in some animal liver microsomes. The primary enzymes involved in the oxidized and demethylated metabolism of these gingerols are CYP1A2 and CYP2C19, but their affinities for gingerols are not the same. CYP2D6 and CYP2B6 contributed significantly to the formation of (3R,5S)-[8]-gingerdiol and (3R,5S)-[10]-gingerdiol, respectively; however, the enzyme responsible for the production of (3R,5S)-[6]-gingerediol is yet to be identified. Some metabolites in microsomes cannot be detected by the 12 investigated CYP enzymes, which may be related to the combined effects of multiple enzymes in microsomes, the different affinity of mixed liver microsomes and CYP enzymes, gene polymorphisms, etc. Overall, this work provides a deeper knowledge of the influence of CYP metabolism on the gingerols, as well as the mode of action and the possibility for drug-herbal interactions.

In vitro differences in toddalolactone metabolism in various species and its effect on cytochrome P450 expression

CONTEXT

Toddalolactone, the main component of Toddalia asiatica (L.) Lam. (Rutaceae), has anticancer, antihypertension, anti-inflammatory, and antifungal activities.

OBJECTIVE

This study investigated the metabolic characteristics of toddalolactone.

MATERIALS AND METHODS

Toddalolactone metabolic stabilities were investigated by incubating toddalolactone (20 μM) with liver microsomes from humans, rabbits, mice, rats, dogs, minipigs, and monkeys for 0, 30, 60, and 90 min. The CYP isoforms involved in toddalolactone metabolism were characterized based on chemical inhibition studies and screening assays. The effects of toddalolactone (0, 10, and 50 µM) on CYP1A1 and CYP3A5 protein expression were investigated by immunoblotting. After injecting toddalolactone (10 mg/kg), in vivo pharmacokinetic profiles using six Sprague-Dawley rats were investigated by taking 9-time points, including 0, 0.25, 0.5, 0.75, 1, 2, 4, 6 and 8 h.

RESULTS

Monkeys showed the greatest metabolic capacity in CYP-mediated and UGT-mediated reaction systems with short half-lives (T_1/2) of 245 and 66 min, respectively, while T_1/2 of humans in two reaction systems were 673 and 83 min, respectively. CYP1A1 and CYP3A5 were the major CYP isoforms involved in toddalolactone biotransformation. Induction of CYP1A1 protein expression by 50 μM toddalolactone was approximately 50% greater than that of the control (0 μM). Peak plasma concentration (C_max) for toddalolactone was 0.42 μg/mL, and T_max occurred at 0.25 h post-dosing. The elimination t_1/2 was 1.05 h, and the AUC_0-t was 0.46 μg/mL/h.

CONCLUSIONS

These findings demonstrated the significant species differences of toddalolactone metabolic profiles, which will promote appropriate species selection in further toddalolactone studies.

Species Difference in the Metabolism of Mulberrin in Vitro and Its Inhibitory Effect on Cytochrome P450 and UDP-Glucuronosyltransferase Enzymes

This study aimed to evaluate the interspecies difference in metabolism of mulberrin and examine the interaction between mulberrin and CYP enzymes or recombinant human uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT) enzymes. Liver microsomes from human (HLMs), Beagle dog (DLMs), minipig (PLMs), monkey (MLMs), rabbit (RLMs), rat (RAMs), and mouse (MIMs) were used to investigate metabolic diversity among different species. Additionally, recombinant human supersomes were used to confirm that metabolic enzymes are involved in the biotransformation of mulberrin. We also evaluated the influence of mulberrin on protein expression by Western blot analysis. Mulberrin metabolism showed significant interspecies differences. We found four and two metabolites in phase I and II reaction systems, respectively. In phase I metabolism profiles of mulberrin for HLMs, PLMs and MLMs conformed to the classic Michaelis-Menten kinetics, RAMs and MIMs followed biphasic kinetics; phase II reaction of mulberrin in HLMs, DLMs, PLMs, MLMs, RLMs, RAMs and MIMs followed biphasic kinetics. UGT1A1 were the major CYP isoforms responsible for the metabolism of mulberrin. Mulberrin showed potent inhibitory effects against CYP3A4, CYP2C9, CYP2E1, UGT1A1, UGT1A3 and UGT2B7 with IC₅₀ values of 54.21, 9.93, 39.12, 3.84, 2.01, 16.36 µM, respectively. According to Western blot analysis, mulberrin can upregulate the protein expression of CYP2C19, and downregulate the expression levels of CYP3A5 and CYP2C9 in HepG2 cells as concentration increased. The interspecies comparisons can help find other species with metabolic pathways similar to those in humans for future in vivo studies.

Investigation on the metabolic characteristics of isobavachin in Psoralea corylifolia L. (Bu-gu-zhi) and its potential inhibition against human cytochrome P450s and UDP-glucuronosyltransferases

OBJECTIVES

Isobavachin is a phenolic with anti-osteoporosis activity. This study aimed to explore its metabolic fates in vivo and in vitro, and to investigate the potential drug-drug interactions involving CYPs and UGTs.

METHODS

Metabolites of isobavachin in mice were first identified and characterized. Oxidation and glucuronidation study were performed using liver and intestine microsomes. Reaction phenotyping, activity correlation analysis and relative activity factor approaches were employed to identify the main CYPs and UGTs involved in isobavachin metabolism. Through kinetic modelling, inhibition mechanisms towards CYPs and UGTs were also explored.

KEY FINDINGS

Two glucuronides (G1 - G2) and three oxidated metabolites (M1 - M3) were identified in mice. Additionally, isobavachin underwent efficient oxidation and glucuronidation by human liver microsomes and HIM with CL_int values from 5.53 to 148.79 μl/min per mg. CYP1A2, 2C19 contributed 11.3% and 17.1% to hepatic metabolism of isobavachin, respectively, with CL_int values from 8.75 to 77.33 μl/min per mg. UGT1As displayed CL_int values from 10.73 to 202.62 μl/min per mg for glucuronidation. Besides, significant correlation analysis also proved that CYP1A2, 2C19 and UGT1A1, 1A9 were main contributors for the metabolism of isobavachin. Furthermore, mice may be the appropriate animal model for predicting its metabolism in human. Moreover, isobavachin exhibited broad inhibition against CYP2B6, 2C9, 2C19, UGT1A1, 1A9, 2B7 with K_i values from 0.05 to 3.05 μm.

CONCLUSIONS

CYP1A2, 2C19 and UGT1As play an important role in isobavachin metabolism. Isobavachin demonstrated broad-spectrum inhibition of CYPs and UGTs.

Metabolic Profiles of Ginger, A Functional Food, and Its Representative Pungent Compounds in Rats by Ultraperformance Liquid Chromatography Coupled with Quadrupole Time-of-Flight Tandem Mass Spectrometry

Ginger, a popular functional food, has been widely used throughout the world for centuries. However, its metabolic behaviors remain unclear, which entails an obstacle to further understanding of its functional components. In this study, the metabolic profiles of ginger in rats were systemically investigated by UPLC-Q/TOF-MS. The results included the characterization of 92 components of ginger based on the summarized fragmentation patterns and self-building chemical database. Furthermore, four representative compounds were selected to explore the typical metabolic pathways of ginger. Consequently, 141 ginger-related xenobiotics were characterized, following the metabolic spots of the pungent phytochemicals were summarized. These findings indicated that the in vivo effective components of ginger were mainly derived from [6]-gingerol and [6]-shogaol. Meanwhile, hydrogenation, demethylation, glucuronidation, sulfation, and thiolation were their major metabolic reactions. These results expand our knowledge about the metabolism of ginger, which will be important for discovering its functional components and the further mechanism research.

Glucuronidation of [6]-shogaol, [8]-shogaol and [10]-shogaol by human tissues and expressed UGT enzymes: identification of UGT2B7 as the major contributor

Shogaols, mainly [6]-shogaol (6S), [8]-shogaol (8S) and [10]-shogaol (10S), the predominant and characteristic pungent phytochemicals in ginger, are responsible for most of its beneficial effects. However, poor oral bioavailability owing to extensive glucuronidation limits their application. The present study aimed to characterize the glucuronidation pathways of 6S, 8S and 10S by using pooled human liver microsomes (HLM), human intestine microsomes (HIM) and recombinant human UDP-glucosyltransferases (UGTs). The rates of glucuronidation were determined by incubating shogaols with uridine diphosphate glucuronic acid-supplemented microsomes. Kinetic parameters were derived by appropriate model fitting. Reaction phenotyping assays, activity correlation analyses and relative activity factors were performed to identify the main UGT isoforms. As a result, one mono-4′-O-glucuronide was detected after incubating each shogaol with HLM and HIM. Enzymes kinetic analysis demonstrated that glucuronidation of shogaols consistently displayed the substrate inhibition profile, and the liver showed higher metabolic activity for shogaols (CL_int = 1.37–2.87 mL min⁻¹ mg⁻¹) than the intestine (CL_int = 0.67–0.85 mL min⁻¹ mg⁻¹). Besides, reaction phenotyping assays revealed that UGT2B7 displayed the highest catalytic ability (CL_int = 0.47–1.17 mL min⁻¹ mg⁻¹) among all tested UGTs. In addition, glucuronidation of shogaols was strongly correlated with AZT glucuronidation (r = 0.886, 0.803 and 0.871 for glucuronidation of 6S, 8S and 10S, respectively; p < 0.01) in a bank of individual HLMs (n = 9). Furthermore, UGT2B7 contributed to 40.8%, 34.2% and 36.0% for the glucuronidation of 6S, 8S and 10S in HLM, respectively. Taken altogether, shogaols were efficiently metabolized through the glucuronidation pathway, and UGT2B7 was the main contributor to their glucuronidation.

The glucuronidation pathways of shogaols ([6]-shogaol, [8]-shogaol and [10]-shogaol) were characterized in human tissues and recombinant human UDP-glucosyltransferases, and UGT2B7 was identified as the main contributor to their glucuronidation.

UGT1A polymorphisms as genetic biomarkers for hepatocellular carcinoma risk in Caucasian population

BACKGROUND & AIMS

The definition of new biomarkers of hepatocellular carcinoma (HCC) risk, especially in high-risk HBV/HCV-positive population, is urgently needed to improve HCC clinical management. This study focused on variants of UDP-glucuronosyltransferase 1A (UGT1A) enzymes that catalyse the reaction of glucuronidation, one of the most important chemical defence pathway of the body. The aim of this study was to elucidate the contribution of UGT1A polymorphisms in predicting HCC susceptibility in Caucasians.

METHODS

In this retrospective case-control analysis, 192 HCC liver transplanted patients represent the study group. Two age/sex-matched groups were used as control, one composed of 167 HBV- and/or HCV-infected individuals, and the other of 192 healthy subjects. All the cases were characterized for a panel of UGT1A1, UGT1A7 and UGT1A9 variants. The study end-point was the association between UGT1A markers and HCC onset.

RESULTS

UGT1A7*3 allele emerged as a protective marker for HCC development among both high-risk HBV/HCV-positive patients (OR=0.64, P=.0026), and healthy subjects (OR=0.47, P=.0051). UGT1A1*28 (OR=0.61, P=.0013) and UGT1A9*22 (OR=2.18, P=.0003) alleles were also associated to HCC occurrence, especially among healthy subjects. UGT1A haplotype, summarizing the UGT1A genetic alterations, confirmed the protective role against HCC development emerged for low-activity alleles. The observed associations could probably be linked to an increase of serum levels of health-beneficial molecules including free bilirubin.

CONCLUSION

A predictive effect of UGT1A polymorphisms on HCC risk was identified. If confirmed, these findings could contribute to improve the HCC surveillance, treatment tailoring and patients care.

Alamethicin for using in bioavailability studies? - Re-evaluation of its effect

A major pathway for the elimination of drugs is the biliary and renal excretion following the formation of more hydrophilic secondary metabolites such as glucuronides. For in vitro investigations of the phase II metabolism, hepatic microsomes are commonly used in the combination with the pore-forming peptide alamethicin, also to give estimates for the in vivo situation. Thus, alamethicin may represent a neglected parameter in the characterization of microsomal in vitro assays. In the present study, the influence of varying alamethicin concentrations on glucuronide formation of selected phenolic compounds was investigated systematically. A correlation between the alamethicin impact and the lipophilicity of the investigated substrates was analyzed as well. Lipophilicity was determined by the logarithm of the octanol-water partition coefficient. For every substrate, a distinct alamethicin concentration could be detected leading to a maximal glucuronidation activity. Further increase of the alamethicin application led to negative effects. The differences between the maximum depletion rates with and without alamethicin addition varied between 2.7% and 18.2% depending on the substrate. A dependence on the lipophilicity could not be confirmed. Calculation of the apparent intrinsic clearance led to a more than 2-fold increase using the most effective alamethicin concentration compared to the alamethicin free control.

Regioselective Glucuronidation of Diosmetin and Chrysoeriol by the Interplay of Glucuronidation and Transport in UGT1A9-Overexpressing HeLa Cells

This study aimed to determine the reaction kinetics of the regioselective glucuronidation of diosmetin and chrysoeriol, two important methylated metabolites of luteolin, by human liver microsomes (HLMs) and uridine-5′-diphosphate glucuronosyltransferase (UGTs) enzymes. This study also investigated the effects of breast cancer resistance protein (BCRP) on the efflux of diosmetin and chrysoeriol glucuronides in HeLa cells overexpressing UGT1A9 (HeLa—UGT1A9). After incubation with HLMs in the presence of UDP-glucuronic acid, diosmetin and chrysoeriol gained two glucuronides each, and the OH—in each B ring of diosmetin and chrysoeriol was the preferable site for glucuronidation. Screening assays with 12 human expressed UGT enzymes and chemical-inhibition assays demonstrated that glucuronide formation was almost exclusively catalyzed by UGT1A1, UGT1A6, and UGT1A9. Importantly, in HeLa—UGT1A9, Ko143 significantly inhibited the efflux of diosmetin and chrysoeriol glucuronides and increased their intracellular levels in a dose-dependent manner. This observation suggested that BCRP-mediated excretion was the predominant pathway for diosmetin and chrysoeriol disposition. In conclusion, UGT1A1, UGT1A6, and UGT1A9 were the chief contributors to the regioselective glucuronidation of diosmetin and chrysoeriol in the liver. Moreover, cellular glucuronidation was significantly altered by inhibiting BCRP, revealing a notable interplay between glucuronidation and efflux transport. Diosmetin and chrysoeriol possibly have different effects on anti-cancer due to the difference of UGT isoforms in different cancer cells.

Structure- and isoform-specific glucuronidation of six curcumin analogs

1. In the present study, we aimed to characterize the glucuronidation of six curcumin analogs (i.e. RAO-3, RAO-8, RAO-9, RAO-18, RAO-19, and RAO-23) derived from galangal using human liver microsomes (HLM) and twelve expressed UGT enzymes. 2. Formation of glucuronide was confirmed using high-resolution mass spectrometry. Single glucuronide metabolite was generated from each of six curcumin analogs. The fragmentation patterns were analyzed and were found to differ significantly between alcoholic and phenolic glucuronides. 3. All six curcumin analogs except one (RAO-23) underwent significant glucuronidation in HLM and expressed UGT enzymes. In general, the methoxy group (close to the phenolic hydroxyl group) enhanced the glucuronidation liability of the curcumin analogs. 4. UGT1A9 and UGT2B7 were primarily responsible for the glucuronidation of two alcoholic analogs (RAO-3 and RAO-18). By contrast, UGT1A9 and four UGT2Bs (UGT2B4, 2B7, 2B15 and 2B17) played important roles in conjugating three phenolic analogs (RAO-8, RAO-9, and RAO-19). Interestingly, the conjugated double bonds system (in the aliphatic chain) was crucial to the substrate selectivity of gastrointestinal UGTs (i.e. UGT1A7, 1A8 and 1A10). 5. In conclusion, glucuronidation of six curcumin analogs from galangal were structure- and isoform-specific. The knowledge should be useful in identifying a curcumin analog with improved metabolic property.