Species differences in pregnane X receptor activation by Δ-9-tetrahydrocannabinol, cannabidiol, and cannabinol

Cannabis plants containing numerous chemicals, including phytocannabinoids, such as Δ-9-tetrahydrocannabinol (THC), cannabidiol (CBD), and cannabinol (CBN). Pregnane X receptor (PXR; gene designation NR1I2) is a nuclear receptor that controls the expression of many genes, including those encoding drug-metabolizing enzymes (e.g., CYP3A4). According to a previous study performed in human hepatocytes in culture, THC and CBD increased CYP3A4 mRNA and enzyme activity levels. The present study was designed to test the hypothesis that THC, CBD, and CBN are PXR agonists. Our concentration-response data demonstrated that THC (10 μM) activated human PXR (hPXR), rat PXR (rPXR), and mouse PXR (mPXR) by 28-fold, 9-fold, and 4-fold, respectively, in hPXR-, rPXR-, or mPXR-transfected HepG2 cells, as determined in dual-luciferase reporter gene assays. By comparison, CBD (10 μM) activated hPXR, rPXR, and mPXR by 23-fold, 6-fold, and 3-fold, respectively, whereas CBN (10 μM) activated hPXR, rPXR, and mPXR by 17-fold, 4-fold, and 3-fold, respectively. The minimum effective concentration (MEC) for hPXR activation by THC, CBD, and CBN was 0.3 μM, which was 10 or 33-fold less than the MEC for rPXR and mPXR activation by these chemicals. Mammalian one-hybrid and two-hybrid assays provided evidence for transactivation of the ligand-binding domain of hPXR and recruitment of steroid receptor coactivator-1 to the ligand-binding domain of hPXR, respectively, by THC, CBD, and CBN. In conclusion, our novel finding indicates hPXR agonism by THC, CBD, and CBN, with preferential activation of hPXR over rPXR and mPXR.