Identification and characterization of the structure–activity relationships involved in UGT1A1 inhibition by anthraquinone and dianthrone constituents of Polygonum multiflorum

Abstract

The adverse effects of Polygonum (P.) multiflorum, including abnormal bilirubin metabolism, are a serious public health issue. As uridine diphosphate (UDP)-glucuronosyltransferase 1A1 (UGT1A1) is the only enzyme responsible for bilirubin metabolism, we investigated the inhibitory effect of a P. multiflorum extract and 10 anthraquinone and dianthrone compounds on UGT1A1 in rat liver microsomes in vitro. The P. multiflorum extract exhibited the strongest inhibitory effect on UGT1A1 activity (inhibition constant [Ki] = 0.3257 μM, 1422 μg of material/mL), followed by cis-emodin dianthrones (Ki = 0.8630 μM), trans-emodin dianthrones (Ki = 1.083 μM), emodin-8-O-glc (Ki = 3.425 μM), and polygonumnolide C2 (Ki = 4.291 μM). Analysis of the structure–activity relationships of these compounds suggested that the spatial orientation of the molecules and the presence of particular functional groups affect UGT1A1 inhibition. A mechanistic analysis showed that all the tested compounds docked into two of the nine active sites of UGT1A1 and suggested that hydrophobic interactions and hydrogen bonds are important for the affinity of the tested compounds for UGT1A1; moreover, their interaction energies were generally in agreement with the Ki values. These findings provide insight into adverse reactions to P. multiflorum and identify the pharmacophores involved in inhibition of UGT1A1.

Recent progress and challenges in screening and characterization of UGT1A1 inhibitors

“…Quinones that display inhibitory effects on UGT1A1 are listed in Table 10 19 , 101 , 110 , 111 . It was recently demonstrated that 10 major quinone constituents of Polygonum multiforum , namely cis- emodindianthrones, trans- emodindianthrones, emodin-8- O -glc, polygonumnolide C2, emodin, polygonumnolide C3, citreorosein, polygonumnolide C4, physcion, and rhein, are naturally occurring potent inhibitors of UGT1A1, with K i values between 0.863 to 127.3 μmol/L 19 . The inhibition of UGT1A1 activity by these quinones might be one of the reasons for P. multiforum -associated adverse effects, particularly elevated bilirubin levels and liver injury 19 .…”

“…It was recently demonstrated that 10 major quinone constituents of Polygonum multiforum , namely cis- emodindianthrones, trans- emodindianthrones, emodin-8- O -glc, polygonumnolide C2, emodin, polygonumnolide C3, citreorosein, polygonumnolide C4, physcion, and rhein, are naturally occurring potent inhibitors of UGT1A1, with K i values between 0.863 to 127.3 μmol/L 19 . The inhibition of UGT1A1 activity by these quinones might be one of the reasons for P. multiforum -associated adverse effects, particularly elevated bilirubin levels and liver injury 19 . Another study demonstrated that emodin competitively inhibited UGT1A1 activity in three model systems, HLM, RLM and recombinant UGT1A1, with K i values of 5.40, 10.02 and 4.85 μmol/L, respectively 110 .…”

“… Inhibitor Substrate Enzyme source IC 50 (μmol/L) K i (μmol/L) Inhibition type Ref. cis -Emodin dianthrones Bilirubin RLM – 0.8630 Competitive 19 trans- Emodin dianthrones Bilirubin RLM – 1.083 Competitive Emodin-8- O -glc Bilirubin RLM 3.425 Competitive Polygonumnolide C2 Bilirubin RLM – 4.291 Non-competitive Polygonumnolide C3 Bilirubin RLM – 12.89 Non-competitive Polygonumnolide C4 Bilirubin RLM – 77.42 Un-competitive Physcion Bilirubin RLM – 94.75 Non-competitive Emodin Bilirubin RLM – 10.01 Competitive Rhein Bilirubin RLM – 127.3 Mixed Citreorosein Bilirubin RLM – 18.56 Mixed Emodin Bilirubin UGT1A1 – 4.85 Competitive 110 Bilirubin HLM – 5.40 Competitive Bilirubin RLM – 10.02 …”

Prediction of Drug-Induced Hyperbilirubinemia by In Vitro Testing

“…UGT1A1 is usually tested in human liver microsomes with β-estradiol as a probe substrate [27,59] and the amount of estradiol-3-glucuronide is determined by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) [60]. UGT1A1-containing microsomes can also be prepared from human cell lines [61] or baculovirus-infected insect cells overexpressing human UGT1A1 [62], and bilirubin [63] or etoposide [64] can be used as alternative substrates in inhibition studies.…”

Advances in the Study of the Potential Hepatotoxic Components and Mechanism of Polygonum multiflorum

“…AQs and anthranone from PM, such as emodin and chrysophanol, significantly inhibited the activity of the bile salt export pump (Bsep), multidrug resistance-associated protein 2 (Mrp2), and basolateral efflux transporters; downregulated the activity of Na+/taurocholate cotransporting polypeptide (Ntcp) [ 44 ]; altered bile acid (BA) disposition; and resulted in liver injury. While anthraquinone and dianthrone exhibited the strongest inhibitory effect on UGT1A1 activity [ 34 , 45 , 46 ], UGT1A1 is an important UGT isoform involved in the metabolic clearance of bilirubin, which is a toxic waste product of heme degradation [ 47 ]. The inhibition of UGT1A1 may lead to bilirubin accumulation, which could induce jaundice, liver injury, etc.…”