Identification and characterization of human UDP-glucuronosyltransferases responsible for the in vitro glucuronidation of ursolic acid

Analysis of A Major Metabolite of Ursolic Acid— Ursolic Acid Sulfate, and Its Quantitative Determination on LC/MS in Human Liver Homogenate

Ursolic acid (UA) is a naturally occurring pentacyclic triterpenoid that exhibits extensive pre-systemic metabolism from in vitro studies. However, there are no available authentic metabolite standards or validated analytical methods to quantitate UA metabolites. We have identified ursolic acid sulfate (UAS) as one of the major metabolites. We were able to identify and characterize its structure via comparison to the chemically synthesized UAS. A cyano (CN, 150 × 4.6 mm, 5 µm) column along with a gradient elution of acetonitrile and 0.08% (v/v) acetic acid, pH 3.0 were employed for chromatographic separation. Negative single ion recording mode (SIR) with electron-spray ionization (ESI) source at mass-to-charge ratios of 455.3 and 535.3 were monitored for UA and UAS, respectively. UAS linearity range was 0.010-2.500 µM. The absolute values of intra-day and inter-day precision (CV, %) and accuracy (DFN, %) were all below 15%. Thus, the analytical method has been validated in the human subcellular fractions to facilitate in vitro/ in vivo DMPK and future clinical disposition studies on UA.

Current trends in drug metabolism and pharmacokinetics

Pharmacokinetics (PK) is the study of the absorption, distribution, metabolism, and excretion (ADME) processes of a drug. Understanding PK properties is essential for drug development and precision medication. In this review we provided an overview of recent research on PK with focus on the following aspects: (1) an update on drug-metabolizing enzymes and transporters in the determination of PK, as well as advances in xenobiotic receptors and noncoding RNAs (ncRNAs) in the modulation of PK, providing new understanding of the transcriptional and posttranscriptional regulatory mechanisms that result in inter-individual variations in pharmacotherapy; (2) current status and trends in assessing drug-drug interactions, especially interactions between drugs and herbs, between drugs and therapeutic biologics, and microbiota-mediated interactions; (3) advances in understanding the effects of diseases on PK, particularly changes in metabolizing enzymes and transporters with disease progression; (4) trends in mathematical modeling including physiologically-based PK modeling and novel animal models such as CRISPR/Cas9-based animal models for DMPK studies; (5) emerging non-classical xenobiotic metabolic pathways and the involvement of novel metabolic enzymes, especially non-P450s. Existing challenges and perspectives on future directions are discussed, and may stimulate the development of new research models, technologies, and strategies towards the development of better drugs and improved clinical practice.

Oleanolic Acid and Ursolic Acid Induce UGT1A1 Expression in HepG2 Cells by Activating PXR Rather Than CAR

Background: Oleanolic acid (OA) and its isomer ursolic acid (UA) have recently emerged as research foci based on their biologic activities. We previously demonstrated that UA can inhibit the activities of UGT1A3 and UGT1A4, and OA inhibits UGT1A3 activity in liver microsomes. However, whether OA and UA affect the expression of UGT1As in HepG2 cells and the underlying regulatory mechanism remain unclear.

Purpose: The present study aimed to explore the effect of OA and UA on the expression of UGT1As in HepG2 cells and the regulatory mechanisms on UGT1A1 based on the pregnane X receptor (PXR) and constitutive androstane receptor (CAR) signaling pathways.

Methods: We analyzed the effect of OA and UA on UGT1A expression and on the PXR/CAR regulatory pathway in HepG2 cells, hPXR-silenced HepG2 cells, and hCAR-silenced HepG2 cells by Q-PCR, Western blotting, and dual-luciferase reporter gene assays.

Results: In HepG2 cells, OA and UA both significantly induced the expression of UGT1A1, UGT1A3, UGT1A4, and UGT1A9 and upregulated the expression of PXR. However, OA and UA did not affect CAR expression. A dual-luciferase reporter assay showed that OA and UA could markedly promote PXR-mediated UGT1A1 luciferase activity, whereas OA and UA did not affect CAR-mediated UGT1A1 luciferase activity. In hPXR-silenced HepG2 cells, OA and UA did not elevate UGT1A1 activity compared to the control group. However, the expression of UGT1A1 in hCAR-silenced HepG2 cells was markedly elevated compared to the control group or with non-silenced HepG2 cells treated with OA (10, 20, and 40 μM) or UA (10, 20, and 40 μM).

Conclusions: OA and UA significantly induce the expression of UGT1A1, UGT1A3, UGT1A4, and UGT1A9 in HepG2 cells, and their induction on UGT1A1 is mediated by PXR activation, not CAR.