Abstract
BACKGROUND AND PURPOSE: P-glycoprotein (P-gp) is an important efflux transporter that supports the barrier function of the gut against invading antigens and against administered drugs. Since glucocorticoids, such as budesonide, are frequently used during inflammatory bowel disease we investigated how budesonide influences P-gp expression in different intestinal cell lines. EXPERIMENTAL APPROACH: LS180 and Caco-2 cells were incubated with budesonide and changes in P-gp expression were determined on mRNA, protein and functional level. The mRNA expression levels of glucocorticoid receptor (GR) and pregnane X receptor (PXR) were determined in these cell lines. PXR receptor was transiently transfected into Caco-2 cells. KEY RESULTS: Budesonide showed an induction of P-gp in LS180 cells and a down-regulation in Caco-2 cells. Expression levels of nuclear receptors revealed high expression of PXR only in LS180 cells and exclusive expression of GR in Caco-2 cells. Mifepristone, an anti-glucocorticoid, could not reverse the down-regulation of P-gp by budesonide in Caco-2 cells. In PXR-transfected Caco-2 cells the budesonide-mediated down-regulation of P-gp was abolished. Furthermore the expression of cytochrome P450 3A4 (CYP3A4), another PXR target gene, was induced in PXR-transfected Caco-2 cells after budesonide treatment. CONCLUSIONS AND IMPLICATIONS: Budesonide has the potential to influence MDR1 expression in vitro. In LS180 cells, the induction of MDR1 by budesonide probably is mediated via PXR. The mechanism of the down-regulation in Caco-2 cells still remains unclear, but GR does not seem to be involved. Further studies are required to evaluate how budesonide alters P-gp expression in vivo.