Discovery of anthraquinones as DPP-IV inhibitors: Structure-activity relationships and inhibitory mechanism.

Dipeptidyl peptidase IV (DPP-IV) is an integrated type II transmembrane protein that reduces endogenous insulin contents and increases plasma glucose levels by hydrolyzing glucagon-like peptide-1 (GLP-1). Inhibition of DPP-IV regulates and maintains glucose homeostasis, making it an attractive drug target for the treatment of diabetes II. Natural compounds have tremendous potential to regulate glucose metabolism. In this study, we examined the DPP-IV inhibitory activity of a series of natural anthraquinones and synthetic structural analogues on DPP-IV using fluorescence-based biochemical assays. The inhibitory efficiency differed among anthraquinone compounds with different structures. Alizarin (7), aloe emodin (11), emodin (13) emerged the outstanding inhibitory potential for DPP-IV with IC50 values lower than 5 µM. To clarifying the inhibitory mechanism, inhibitory kinetics were performed, which showed that alizarin red S (8) and 13 were effective non-competitive inhibitors of DPP-IV, while alizarin complexone (9), rhein (12), and anthraquinone-2-carboxylic acid (23) were mixed inhibitors. Emodin was determined as inhibitor with the strongest DPP-IV-binding affinity determined via molecular docking. Structure-activity relationship (SAR) demonstrated that hydroxyl group at C-1 and C-8 sites and hydroxyl, hydroxymethyl or carboxyl group at the C-2 or C-3 site were very essential for DPP-IV inhibition, replacement of hydroxyl group with amino group at C-1 could led to an increase of the inhibitory potential. Further fluorescence imaging showed that both compounds 7 and 13 significantly inhibited DPP-IV activity in RTPEC cells. Overall, the results indicated that anthraquinones would be a natural functional ingredient for inhibiting DPP-IV and provided new ideas for searching and developing potential antidiabetic compounds.

Inhibition of drug-metabolizing enzymes by Jingyin granules: implications of herb-drug interactions in antiviral therapy.

Jingyin granules, a marketed antiviral herbal medicine, have been recommended for treating H1N1 influenza A virus infection and Coronavirus disease 2019 (COVID-19) in China. To fight viral diseases in a more efficient way, Jingyin granules are frequently co-administered in clinical settings with a variety of therapeutic agents, including antiviral drugs, anti-inflammatory drugs, and other Western medicines. However, it is unclear whether Jingyin granules modulate the pharmacokinetics of Western drugs or trigger clinically significant herb-drug interactions. This study aims to assess the inhibitory potency of the herbal extract of Jingyin granules (HEJG) against human drug-metabolizing enzymes and to clarify whether HEJG can modulate the pharmacokinetic profiles of Western drug(s) in vivo. The results clearly demonstrated that HEJG dose-dependently inhibited human CES1A, CES2A, CYPs1A, 2A6, 2C8, 2C9, 2D6, and 2E1; this herbal medicine also time- and NADPH-dependently inhibited human CYP2C19 and CYP3A. In vivo tests showed that HEJG significantly increased the plasma exposure of lopinavir (a CYP3A-substrate drug) by 2.43-fold and strongly prolonged its half-life by 1.91-fold when HEJG (3 g/kg) was co-administered with lopinavir to rats. Further investigation revealed licochalcone A, licochalcone B, licochalcone C and echinatin in Radix Glycyrrhizae, as well as quercetin and kaempferol in Folium Llicis Purpureae, to be time-dependent CYP3A inhibitors. Collectively, our findings reveal that HEJG modulates the pharmacokinetics of CYP substrate-drug(s) by inactivating CYP3A, providing key information for both clinicians and patients to use herb-drug combinations for antiviral therapy in a scientific and reasonable way.

Carboxylesterase inhibitors from clinically available medicines and their impact on drug metabolism.

Mammalian carboxylesterases (CES), the key members of the serine hydrolase superfamily, hydrolyze a wide range of endogenous substances and xenobiotics bearing ester or amide bond(s). In humans, most of identified CES are segregated into the CES1A and CES2A subfamilies. Strong inhibition on human CES (including hCES1A and hCES2A) may modulate pharmacokinetic profiles of CES-substrate drugs, thereby changing the pharmacological and toxicological responses of these drugs. This review covered recent advances in discovery of hCES inhibitors from clinically available medications, as well as their impact on CES-associated drug metabolism. Three comprehensive lists of hCES inhibitors deriving from clinically available medications including therapeutic drugs, pharmaceutical excipients and herbal medicines, alongside with their inhibition potentials and inhibition parameters, are summarized. Furthermore, the potential risks of hCES inhibitors to trigger drug/herb-drug interactions (DDIs/HDIs) and future concerns in this field are highlighted. Potent hCES inhibitors may trigger clinically relevant DDIs/HDIs, especially when these inhibitors are co-administrated with CES substrate-drugs with very narrow therapeutic windows. All data and knowledge presented here provide key information for the clinicians to assess the risks of clinically available hCES inhibitors on drug metabolism. In future, more practical and highly specific substrates for hCES1A/hCES2A should be developed and used for studies on CES-mediated DDIs/HDIs both in vitro and in vivo.

Discovery of natural pentacyclic triterpenoids as potent and selective inhibitors against human carboxylesterase 1.

Human carboxylesterase 1 (CES1), primarily expressed in the liver and adipocytes, is responsible for the hydrolysis of endogenous esters (such as cholesteryl esters and triacylglycerols) and the metabolism of xenobiotic esters (such as clopidogrel and oseltamivir), thus participates in physiological and pathological processes. In this study, a series of natural pentacyclic triterpenoids were collected and their inhibitory effects against CES1 and CES2 were assayed using D-luciferin methyl ester (DME) and N-(2-butyl-1,3-dioxo-2,3-dihydro-1H-benzo[de] isoquinolin- 6-yl)- 2-chloroacetamide (NCEN) as specific optical substrate for CES1, and CES2, respectively. To this end, betulinic acid (BA) was found with strong inhibitory effect on CES1 (IC50, 15 nM) and relative high selectivity over CES2 (>2400-fold). Primary structure-activity relationships (SAR) analysis and docking simulations revealed that the carboxyl group at the C-28 site of BA is very essential for CES1 inhibition. The inhibition kinetic analyses demonstrated that BA was a potent competitive inhibitor against CES1-mediated DME hydrolysis. Further investigation on the inhibitory effect of BA in living cells (HepG2) based assays demonstrated that BA displayed potent inhibitory effects on intracellular CES1 activities, with the low IC50 value of 1.30 µM. These results demonstrated that BA is potent and highly selective CES1 inhibitor, which might be used as the promising tool for exploring the biological functions of CES1 in complex biological systems.

A Practical and High-Affinity Fluorescent Probe for Uridine Diphosphate Glucuronosyltransferase 1A1: A Good Surrogate for Bilirubin.

This study aimed to develop a practical and high-affinity fluorescent probe for uridine diphosphate glucuronosyltransferase 1A1 (UGT1A1), a key conjugative enzyme responsible for the elimination and detoxification of many potentially harmful compounds. Several substrates derived from N-butyl-4-phenyl-1,8-naphthalimide were designed and synthesized on the basis of the substrate preference of UGT1A1 and the principle of photoinduced electron transfer (PET). Following the preliminary screening, substrate 2 was found with a high specificity and high affinity toward UGT1A1, while such biotransformation brought remarkable changes in fluorescence emission. Both inhibition kinetic analyses and molecular docking simulations demonstrated that 2 could bind on UGT1A1 at the same ligand-binding site as bilirubin. Furthermore, this newly developed probe was successfully used for sensing UGT1A1 activities and the high-throughput screening of UGT1A1 modulators in complex biological samples. In conclusion, a practical and high-affinity fluorescent probe for UGT1A1 was designed and well-characterized, which could serve as a good surrogate for bilirubin to investigate UGT1A1-ligand interactions.

Recent progress in the discovery of natural inhibitors against human carboxylesterases.

Mammalian carboxylesterases (CEs) are important serine hydrolases catalyzing the hydrolysis of ester- or amide-containing compounds into the corresponding alcohols and carboxylic acids. In human, two primary carboxylesterases including hCE1 and hCE2 have been identified and extensively studied in the past decade. hCE1 is known to play crucial roles in the metabolism of a wide variety of endogenous esters, clinical drugs and insecticides, while hCE2 plays a key role in the metabolic activation of anticancer agents including irinotecan and capecitabine. The key roles of hCEs in both human health and xenobiotic metabolism arouse great interest in the discovery of potent and selective hCEs inhibitors to modulate endobiotic metabolism or to improve the outcomes of patients administrated with ester drugs. This review covers the significance and recent progress in the discovery of natural inhibitors against hCEs. The tools for screening and characterization of inhibitors against human CEs, including traditional LC-based approaches and the newly developed optical substrate-based assays, are summarized and discussed for the first time. Furthermore, the structural information and inhibitory capacities of all reported hCEs inhibitors including fatty acids, flavonoids, tanshinones and triterpenoids have been systematically summarized. All information and knowledge presented in this review will be very helpful for medicinal chemists to develop more potent and highly selective inhibitors against hCEs for potential biomedical applications.

Interspecies variation in phase I metabolism of bufalin in hepatic microsomes from mouse, rat, dog, minipig, monkey, and human.

1. Bufalin (BF), one of the major bioactive compounds in traditional Chinese medicine (TCM) Chansu, has been found with various pharmacological and toxicological effects. This study aims to investigate the species differences in phase I metabolism of BF in hepatic microsomes from human and five common experimental animals. 2. Metabolite profiling demonstrated that two major metabolites were formed in liver microsomes from human and animal species in NADPH-generating system. Two major metabolites were identified as 5ß-hydroxyl-bufalin and 3-keto-bufalin, with the help of authentic standards. CYP3A was assigned as the main isoform involved in both 5ß-hydroxylation and 3-oxidation in all studied liver microsomes. The apparent kinetic parameters including substrate affinity and catalytic efficiency for 5ß-hydroxylation and 3-oxidation of BF were also determined. 3. In summary, CYP3A mediated 5ß-hydroxylation and 3-oxidation were two major metabolic pathways of BF in hepatic microsomes from human and five studied animals, but kinetic analysis demonstrated that the intrinsic clearances of these two metabolic pathways were much different among various species. The qualitative and quantitative interspecies study indicated that minipig exhibited the similar metabolic profile, kinetic behaviors and intrinsic metabolic clearances of BF phase I biotransformation in comparison with that of human.