P-209 YI Decreased Pregnane X Receptor (PXR) Expression in Inflamed Versus Non-Inflamed Small Bowel of Children with Crohn’s Disease

Abstract

Human pregnane X receptor (PXR) is a xenobiotic nuclear receptor responsible for transcriptional regulation of specific drug metabolizing enzymes (e.g., CYP3A4) and transporters (e.g., ABCB1). PXR dysregulation has also been implicated in the pathogenesis of IBD in a well-established model of chemically-induced IBD in mice, as well as some human studies. Data on PXR expression in intestinal tissue of pediatric patients with Crohn’s Disease (CD) are limited, with no current conclusive information regarding PXR expression in healthy versus inflamed mucosa. The primary objective of this single center, retrospective, pilot study was to test the hypothesis that PXR expression is decreased in actively inflamed small intestinal tissue from pediatric patients with CD. RNA was extracted from archived formalin-fixed paraffin-embedded (FFPE) intestinal biopsy samples obtained during routine EGD/colonoscopy in pediatric patients, aged 7 to 18 years, with a diagnosis of CD (n = 18) and age- and sex-matched Controls without IBD (n = 12). Tissue samples with adequate mRNA quality, as determined by 3’:5’ GAPDH ratio <10, were included in the analysis of relative mRNA expression of PXR in inflamed terminal ileum (TI) versus non-inflamed duodenum. Quantitative real-time reverse-transcription polymerase chain reaction (RT-qPCR) was used to determine relative mRNA expression. All data are reported as relative expression normalized against GAPDH, an established reference gene in the human small intestine, and are log transformed. Additionally, relative villin expression (an indicator of epithelial cell content) was determined across tissue types and disease states. Differences in relative mRNA expression were explored using a paired t-test; α = 0.05. In the cohort of children with CD, a statistically significant decrease in PXR expression was observed in inflamed TI versus non-inflamed duodenum (relative expression TI=1.88 ± 0.89 versus duodenum = 2.5 ± 0.67; P = 0.0003). In contrast, no difference in PXR expression was observed between non-inflamed TI versus non-inflamed duodenum in Controls (TI=2.11 ± 0.41 versus duodenum = 2.26 ± 0.61; P = 0.52). Similarly, villin expression was significantly decreased in the inflamed TI of children with CD compared to non-inflamed duodenum from the same children (TI = 3.79 ± 0.91 versus duodenum = 4.61 ± 0.52; P = 0.0002). This difference in villin expression was not observed in non-inflamed TI versus non-inflamed duodenum in Controls (TI = 4.30 ± 0.35 versus duodenum = 4.07 ± 0.4; P = 0.26). Finally, GAPDH expression did not differ with age, sex, or location along the small intestine (i.e., TI versus duodenum) in the CD or the Control group. Our findings demonstrate no apparent regional difference in PXR expression in the small intestine of children without IBD. In contrast, our data demonstrate a statistically significant decrease in PXR expression in actively inflamed versus non-inflamed small intestine of pediatric patients with CD. This differential pattern of PXR expression in CD may suggest a potential role for PXR in disease phenotype expression and, potentially, in the regulation of proteins important to drug disposition (i.e., CYP3A4, ABCB1). It is not yet clear how the observed differences in epithelial cell content contribute to the observed decrease in PXR, as the differences themselves may be the result of inflammation or disease state. Additional studies are currently underway.