Commiphora myrrha resin extract-modulated cytochrome P-450 2C9 enzyme expression in cultured Hep G2 cells is associated with resin extract-derived metabolites binding to Pregnane X receptor.

Background: The use of natural health products (NHP) is constantly increasing worldwide. Among the most NHP consumed in the Arabian Peninsula are the resins of Commiphora myrrha (C. myrrha) tree. Consumption of C. myrrha may result in herb-drug interactions mediated by drug-metabolizing cytochrome P-450 (CYP) enzymes in the liver, which could lead to serious health consequences for patients. This study aims to determine the herb-drug interactions based on the induction of predominant CYP 2C9 by a non-toxic boiled aqueous extract of C. myrrha and to unveil the potential involvement of xenobiotic-sensing nuclear receptors such as transcription factor Pregnane X Receptor (PXR) in CYP 2C9 induction, and to predict the molecular interactions of PXR with C. myrrha-derived metabolite(s).

Methods: Cytotoxic effect of boiled aqueous extract of C. myrrha resins in cultured liver carcinoma Hep G2 cells was assessed using MTT assay. CYP 2C9 gene and protein expression levels were evaluated using reverse transcription-quantitative polymerase chain reaction and Western blot. Nuclear receptor binding assays, chemical analysis and molecular docking prediction were performed using specific kits, liquid chromatography-mass spectrometry time-of-flight, and in silico software, respectively.

Results: Tested at low concentrations (0.01-10 µg/mL) devoid of anti-proliferative effects, boiled C. myrrha resin aqueous extract upregulated CYP 2C9 gene and protein expressions in a dose-dependent manner, reaching a mean expression level exceeding 3.0-fold change in Hep G2 cells, compared with the basal level expressed in untreated cells. Furthermore, the use of the nuclear receptor binding assays confirmed the binding between C. myrrha metabolite(s) and PXR, while no binding to the other xenobiotic-sensing nuclear receptor, the constitutive androstane receptor (CAR), was observed. Chemical analysis and computational molecular docking using in silico studies revealed that a few C. myrrha resin-derived metabolites are strongly bound to PXR. In particular, the identified metabolite named commic acid E exhibited a predicted molecular docking score close to that of a native PXR ligand, suggesting C. myrrha metabolite(s) as potential PXR agonists.

Conclusions: Although in vivo studies are needed, this study cautions patients, healthcare providers, and governmental regulators against the consumption of C. myrrha preparations with a high potential for herb-drug interactions through drug-metabolizing CYP 2C9 enzyme induction, which could affect drug efficacy.