P082 Xenobiotic nuclear receptors: linking bile acid signalling to alterations in CYP3A4 metabolism in Crohn's disease

The Cytochrome P450 (CYP) 3A4 is the cornerstone of drug metabolism in humans. The impact of disease on CYP3A4 activity is still incompletely defined. Given the importance of CYP3A4 to the disposition of many clinically-important substrates, including new classes of orally-administered, small-molecule immunomodulators for inflammatory bowel disease and its high concentration in the intestine, understanding the effect of Crohn's disease (CD) on CYP3A4 activity is highly relevant. We aimed to assess the impact of CD on CYP3A4 activity using the endogenous in vivo probe 4β-hydroxycholesterol (4BOHC) and to propose a molecular mechanism for any detectable differences from non-CD controls. Our study was conducted in two parts: in a cross-sectional study of individuals with (n = 74) and without (n = 71) CD, plasma 4BOHC concentrations as well as a plasma bile acid profile of 12 bile acids were determined using liquid chromatography-mass spectrometry. In vitro modelling, employing luciferase transactivation assays, was used to evaluate the effect of differential bile acid profiles (control, inactive and active CD) on the activation of CYP3A4 via nuclear receptors, pregnane X receptor (PXR) and farnesoid X receptor (FXR) in HepG2 cells. The plasma 4BOHC concentrations were higher in the control population vs. the CD population (CD= 18.68 ng/ml ± 13.02 ng/ml, non-CD= 46.38 ng/ml ± 40.70 ng/ml, p ≤ 0.0001). The ratio of plasma bile acids was different between subjects with and without CD and further varied by disease activity. To explore the impact of CD-specific plasma bile acid profiles on PXR and FXR activation, two models were created. In HepG2 cells transfected with hPXR and CYP3A4-pGL3 plasmids (model 1), no difference was seen in the luciferase activity amongst the cells exposed to the cohort-specific bile acid profiles at 25 μM or 50 μM. At 75 μM, bile acid-activated CYP3A4-reporter activities were significantly decreased in the CD cohorts compared with the control cohort, though no difference was seen based on disease activity. To evaluate the effect of CD-specific bile acid signalling on FXR (another CYP3A4 regulator), HepG2 cells were transfected with hFXR and BSEP-pGL3 plasmids (model 2) and exposed to cohort-specific bile acid profiles. At 25 μM and 50 μM, reduced FXR-mediated activation of BSEP was seen with the active CD bile acid profile compared with the control profile. At 75 μM, bile acid-activated BSEP-reporter activity was significantly decreased in the disease state and further so in active disease. Our data show that CYP3A4 activity is decreased in CD and that disease-dependent changes in nuclear receptor-signalling may contribute to CD-dependent variation.