title: Rifaximin is a gut-specific human pregnane X receptor activator.
abstract: Rifaximin, a rifamycin analog approved for the treatment of travelers' diarrhea, is also beneficial in the treatment of multiple chronic gastrointestinal disorders. However, the mechanisms contributing to the effects of rifaximin on chronic gastrointestinal disorders are not fully understood. In the current study, rifaximin was investigated for its role in activation of the pregnane X receptor (PXR), a nuclear receptor that regulates genes involved in xenobiotic and limited endobiotic deposition and detoxication. PXR-humanized (hPXR), Pxr-null, and wild-type mice were treated orally with rifaximin, and rifampicin, a well characterized human PXR ligand. Rifaximin was highly concentrated in the intestinal tract compared with rifampicin. Rifaximin treatment resulted in significant induction of PXR target genes in the intestine of hPXR mice, but not in wild-type and Pxr-null mice. However, rifaximin treatment demonstrated no significant effect on hepatic PXR target genes in wild-type, Pxr-null, and hPXR mice. Consistent with the in vivo data, cell-based reporter gene assay revealed rifaximin-mediated activation of human PXR, but not the other xenobiotic nuclear receptors constitutive androstane receptor, peroxisome proliferator-activated receptor (PPAR)alpha, PPARgamma, and farnesoid X receptor. Pretreatment with rifaximin did not affect the pharmacokinetics of the CYP3A substrate midazolam, but it increased the C(max) and decreased T(max) of 1'-hydroxymidazolam. Collectively, the current study identified rifaximin as a gut-specific human PXR ligand, and it provided further evidence for the utility of hPXR mice as a critical tool for the study of human PXR activators. Further human studies are suggested to assess the potential role of rifaximin-mediated gut PXR activation in therapeutics of chronic gastrointestinal disorders.
authors: Laboratory of Metabolism, Center for Cancer Research, National Cancer Institute, Bldg. 37, Room 3106, Bethesda, MD 20892, USA.
authors: Xiaochao
authors: X
authors: Ma
authors: Yatrik M
authors: YM
authors: Shah
authors: Grace L
authors: GL
authors: Guo
authors: Ting
authors: T
authors: Wang
authors: Kristopher W
authors: KW
authors: Krausz
authors: Jeffrey R
authors: JR
authors: Idle
authors: Frank J
authors: FJ
authors: Gonzalez
mesh_terms: D000818:Animals; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology; D004305:Dose-Response Relationship, Drug; D005765:Gastrointestinal Agents / Q000494:pharmacology*; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects*; D008297:Male; D051379:Mice; D008874:Midazolam / Q000493:pharmacokinetics; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid / Q000187:drug effects* / Q000235:genetics / Q000502:physiology; D012293:Rifampin / Q000494:pharmacology; D012294:Rifamycins / Q000493:pharmacokinetics / Q000494:pharmacology*; D000078262:Rifaximin
chemical_list: D005765:Gastrointestinal Agents; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D012294:Rifamycins; D003577:Cytochrome P-450 Enzyme System; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D000078262:Rifaximin; D008874:Midazolam; D012293:Rifampin