Carotenoids and their metabolites are naturally occurring activators of gene expression via the pregnane X receptor.
Carotenoids are important micronutrients in the human diet and are present in human serum at micromolar concentrations. In addition to their antioxidant potential, carotenoids obtain physiologically relevant properties such as influencing cellular signal pathways, gene expression or induction of detoxifying enzymes. In this study, we determined the transactivation of PXR by cotransfection with the full-length receptor and a PXR-responsive reporter gene. Carotenoids and retinol revealed a 5-6 fold reporter gene activity in HepG2 cells in comparison to a 7-fold induction by the well-known PXR agonist rifampicin, whereas apo-carotenals and lycopene exerted less or no activation potential. The inductive efficacy was hereby concentration-dependent. In addition, carotenoid- or retinol-mediated gene expression of PXR-responsive genes like CYP3A4/CYP3A7, CYP3A5, MDR-1 and MRP-2 has been determined in HepG2 cells by RT-PCR with up-regulative properties of beta-carotene or retinol being comparable to or even higher than that of rifampicin. In conclusion, PXR-mediated up-regulation of CYP3A4/CYP3A7 and CYP3A5 as well as MDR1 and MRP2 by carotenoids points to a potential interference on the metabolism of xenobiotic and endogenous relevant compounds.
Rühl
Ralph
R
Institute of Nutritional Science, University of Potsdam, Arthur-Scheunert-Allee 114-116, 14558 Potsdam-Rehbrücke, Germany. ralphruehl@web.de
Sczech
Ronny
R
Landes
Nico
N
Pfluger
Paul
P
Kluth
Dirk
D
Schweigert
Florian J
FJ
D000975:Antioxidants / Q000494:pharmacology*; D002338:Carotenoids / Q000494:pharmacology*; D015870:Gene Expression / Q000187:drug effects*; D005786:Gene Expression Regulation; D006801:Humans; D000089762:Multidrug Resistance-Associated Protein 2; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000502:physiology; D011987:Receptors, Steroid / Q000187:drug effects* / Q000502:physiology; D015533:Transcriptional Activation; D014407:Tumor Cells, Cultured
C000715087:ABCC2 protein, human; D000975:Antioxidants; D000089762:Multidrug Resistance-Associated Protein 2; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D002338:Carotenoids