Accurate identification of UDP-glucuronosyltransferase 1A1 (UGT1A1) inhibitors using UGT1A1-overexpressing HeLa cells

Identification of naturally occurring inhibitors in Xian-Ling-Gu-Bao capsule against the glucuronidation of estrogens

Xian-Ling-Gu-Bao (XLGB) capsule, a well-known traditional Chinese medicine prescription, is widely used for the treatment of osteoporosis. It could significantly increase the levels of estrogen in ovariectomized rats and mice. However, this working mechanism has not been well elucidated. Considering that UDP-glucuronosyltransferase (UGT) enzymes are the important enzymes that inactivate and regulate estrogen activity in vivo, this study aimed to identify the bioactive compounds from XLGB against the glucuronidation of estrogens. First, thirty compounds were considered as candidate bioactive compounds based on our previous studies including pharmacological evaluation, chemical profiles, and metabolic profiles. Second, the characteristics of estrogen glucuronidation by uridine diphosphate glucuronic acid (UDPGA)-supplemented human liver microsomes (HLM), human intestine microsomes (HIM), and expressed UGT enzymes were determined, and the incubation systems of their key UGT enzymes were optimized. Then, inhibitory effects and mechanisms of XLGB and its main compounds toward the key UGT isozymes were further investigated. As a result, estrogen underwent efficient glucuronidation by HLM and HIM. UGT1A10, 1A1, and 2B7 were mainly responsible for the glucuronidation of estrone, β-estradiol, and estriol, respectively. For E1 and E2, UGT1A10 and 1A1 tended to mediate estrogen-3-O-glucuronidation, while UGT2B7 preferred catalyzing estrogen-16-O-glucuronidation. Furthermore, the incubation system for active UGT isoforms was optimized including Tris-HCl buffer, detergents, MgCl2 concentration, β-glucuronidase inhibitors, UDPGA concentration, protein concentration, and incubation time. Based on optimal incubation conditions, eleven, nine, and nine compounds were identified as the potent inhibitors for UGT1A10, 1A1, and 2B7, respectively (IC50 < 4.97 μM and Ki < 3.35 μM). Among them, six compounds (bavachin, isobavachin, isobavachalcone, neobavaisoflavone, corylifol A, and icariside II) simultaneously demonstrated potent inhibitory effects against these three active enzymes. Prenylated flavanols from Epimedium brevicornu Maxim., prenylated flavonoids from Psoralea corylifolia L., and salvianolic acids from Salvia miltiorrhiza Bge. were characterized as the most important and effective compounds. The identification of potent natural inhibitors of XLGB against the glucuronidation of estrogen laid an important foundation for the pharmacodynamic material basis.

Insights on the Multifunctional Activities of Magnolol

Over years, various biological constituents are isolated from Traditional Chinese Medicine and confirmed to show multifunctional activities. Magnolol, a hydroxylated biphenyl natural compound isolated from Magnolia officinalis, has been extensively documented and shows a range of biological activities. Many signaling pathways include, but are not limited to, NF-κB/MAPK, Nrf2/HO-1, and PI3K/Akt pathways, which are implicated in the biological functions mediated by magnolol. Thus, magnolol is considered as a promising therapeutic agent for clinic research. However, the low water solubility, the low bioavailability, and the rapid metabolism of magnolol dramatically limit its clinical application. In this review, we will comprehensively discuss the last five-year progress of the biological activities of magnolol, including anti-inflammatory, antimicroorganism, antioxidative, anticancer, neuroprotective, cardiovascular protection, metabolism regulation, and ion-mediating activity.

Recent progress and challenges in screening and characterization of UGT1A1 inhibitors

Uridine-diphosphate glucuronosyltransferase 1A1 (UGT1A1) is an important conjugative enzyme in mammals that is responsible for the conjugation and detoxification of both endogenous and xenobiotic compounds. Strong inhibition of UGT1A1 may trigger adverse drug/herb-drug interactions, or result in metabolic disorders of endobiotic metabolism. Therefore, both the US Food and Drug Administration (FDA) and the European Medicines Agency (EMA) have recommended assaying the inhibitory potential of drugs under development on the human UGT1A1 prior to approval. This review focuses on the significance, progress and challenges in discovery and characterization of UGT1A1 inhibitors. Recent advances in the development of UGT1A1 probes and their application for screening UGT1A1 inhibitors are summarized and discussed in this review for the first time. Furthermore, a long list of UGT1A1 inhibitors, including information on their inhibition potency, inhibition mode, and affinity, has been prepared and analyzed. Challenges and future directions in this field are highlighted in the final section. The information and knowledge that are presented in this review provide guidance for rational use of drugs/herbs in order to avoid the occurrence of adverse effects via UGT1A1 inhibition, as well as presenting methods for rapid screening and characterization of UGT1A1 inhibitors and for facilitating investigations on UGT1A1-ligand interactions.

Occurrence, biological activity and metabolism of 6-shogaol

As one of the main bioactive compounds of dried ginger, 6-shogaol has been widely used to alleviate many ailments. It is also a major pungent flavor component, and its precursor prior to dehydration is 6-gingerol, which is reported to be responsible for the pungent flavor and biological activity of fresh ginger. Structurally, gingerols including 6-gingerol have a β-hydroxyl ketone moiety and is liable to dehydrate to generate an α,β-unsaturated ketone under heat and/or acidic conditions. The conjugation of the α,β-unsaturated ketone skeleton in the chemical structure of 6-shogaol explicates its higher potency and efficacy than 6-gingerol in terms of antioxidant, anti-inflammatory, anticancer, antiemetic and other bioactivities. Research on the health benefits of 6-shogaol has been conducted and results have been reported recently; however, scientific data are scattered due to a lack of systematic collection. In addition, action mechanisms of the preventive and/or therapeutic actions of 6-shogaol remain obscurely non-collective. Herein, we review the preparations, biological activity and mechanisms, and metabolism of 6-shogaol as well as the properties of 6-shogaol metabolites.

In vitro characterization of belinostat glucuronidation: demonstration of both UGT1A1 and UGT2B7 as the main contributing isozymes

1. Belinostat is a histone deacetylase inhibitor that has been approved for the treatment of peripheral T-cell lymphoma. This study aimed to identify the UDP-glucuronosyltransferase (UGT) enzymes responsible for belinostat glucuronidation through kinetic determination using recombinant enzymes with determined enzyme concentrations. 2. The rate of glucuronidation was determined by incubation of belinostat with enzyme preparations. Kinetic parameters such as K_m and V_max were derived by fitting an appropriate model to the glucuronidation data. The role of active UGT enzymes to belinostat metabolism was evaluated using inhibition experiments and activity correlation analyses. 3. Human liver microsomes generated a glucuronide metabolite (i.e. belinostat glucuronide) from belinostat. The glucuronide structure was confirmed by high-resolution mass spectrometry as well as the fragmentation pattern. Of 12 test UGT enzymes, only four (UGT1A1, 1A3, 2B4, and 2B7) showed metabolic activities toward belinostat. UGT1A1 was the most active enzyme, followed by UGT2B7, 1A3, and 2B4. Kinetic profiles for UGT1A1, 1A3, 2B4, and 2B7 were well described by Michaelis-Menten, Michaelis-Menten, Hill equation, and substrate inhibition equation, respectively. 4. Glucuronidation of belinostat was markedly inhibited by emodin and apigenin (two potent inhibitors of UGT1A1), and by quinidine and diclofenac sodium (two selective inhibitors of UGT2B7). Belinostat glucuronidation was found to be significantly correlated with β-estradiol 3-O-glucuronidation and zidovudine glucuronidation. 5. It was concluded that in addition to UGT1A1, UGT2B7 was also an important contributor to belinostat glucuronidation.