Metabolomics reveals a novel vitamin E metabolite and attenuated vitamin E metabolism upon PXR activation

Abstract

Pregnane X receptor (PXR) is an important nuclear receptor xenosensor that regulates the expression of metabolic enzymes and transporters involved in the metabolism of xenobiotics and endobiotics. In this study, ultra-performance liquid chromatography (UPLC) coupled with electrospray time-of-flight mass spectrometry (TOFMS), revealed altered urinary metabolomes in both Pxr-null and wild-type mice treated with the mouse PXR activator pregnenolone 16α-carbonitrile (PCN). Multivariate data analysis revealed that PCN significantly attenuated the urinary vitamin E metabolite α-carboxyethyl hydroxychroman (CEHC) glucuronide together with a novel metabolite in wild-type but not Pxr-null mice. Deconjugation experiments with β-glucuronidase and β-glucosidase suggested that the novel urinary metabolite was γ-CEHC β-D-glucoside (Glc). The identity of γ-CEHC Glc was confirmed by chemical synthesis and by comparing tandem mass fragmentation of the urinary metabolite with the authentic standard. The lower urinary CEHC was likely due to PXR-mediated repression of hepatic sterol carrier protein 2 involved in peroxisomal β-oxidation of branched-chain fatty acids (BCFA). Using a combination of metabolomic analysis and a genetically modified mouse model, this study revealed that activation of PXR results in attenuated levels of the two vitamin E conjugates, and identification of a novel vitamin E metabolite, γ-CEHC Glc. Activation of PXR results in attenuated levels of the two vitamin E conjugates that may be useful as biomarkers of PXR activation. Pregnane X receptor (PXR) is an important nuclear receptor xenosensor that regulates the expression of metabolic enzymes and transporters involved in the metabolism of xenobiotics and endobiotics. In this study, ultra-performance liquid chromatography (UPLC) coupled with electrospray time-of-flight mass spectrometry (TOFMS), revealed altered urinary metabolomes in both Pxr-null and wild-type mice treated with the mouse PXR activator pregnenolone 16α-carbonitrile (PCN). Multivariate data analysis revealed that PCN significantly attenuated the urinary vitamin E metabolite α-carboxyethyl hydroxychroman (CEHC) glucuronide together with a novel metabolite in wild-type but not Pxr-null mice. Deconjugation experiments with β-glucuronidase and β-glucosidase suggested that the novel urinary metabolite was γ-CEHC β-D-glucoside (Glc). The identity of γ-CEHC Glc was confirmed by chemical synthesis and by comparing tandem mass fragmentation of the urinary metabolite with the authentic standard. The lower urinary CEHC was likely due to PXR-mediated repression of hepatic sterol carrier protein 2 involved in peroxisomal β-oxidation of branched-chain fatty acids (BCFA). Using a combination of metabolomic analysis and a genetically modified mouse model, this study revealed that activation of PXR results in attenuated levels of the two vitamin E conjugates, and identification of a novel vitamin E metabolite, γ-CEHC Glc. Activation of PXR results in attenuated levels of the two vitamin E conjugates that may be useful as biomarkers of PXR activation. Pregnane X receptor (PXR, NR1I2) is a member of the nuclear receptor superfamily and highly expressed in liver and intestine of mammals. PXR was characterized as a xenosensor that regulates the expression of metabolic enzymes and transporters facilitating elimination of xenobiotics and endogenous toxic chemicals such as bile acids (1Kliewer S.A. Willson T.M. Regulation of xenobiotic and bile acid metabolism by the nuclear pregnane X receptor.J. Lipid Res. 2002; 43: 359-364Abstract Full Text Full Text PDF PubMed Google Scholar). The mechanisms of how PXR regulates numerous genes involved in the metabolism of chemicals have been investigated during the last decade. Results from those studies indicated that PXR activation is dependent on its ligands and PXR direct repeat 4 (DR-4) response elements (PXRE) usually located upstream of target genes. When a ligand binds to PXR, PXR translocates to the nucleus, heterodimerizes with retinoid X receptor (RXR, NR1B) and binds to PXREs. PXR can be activated by structurally diverse chemicals including certain pharmaceuticals, herbal medicines, dietary supplements, environmental pollutants, and endobiotics (2Poso A. Honkakoski P. Ligand recognition by drug-activated nuclear receptors PXR and CAR: structural, site-directed mutagenesis and molecular modeling studies.Mini Rev. Med. Chem. 2006; 6: 937-947Crossref PubMed Scopus (32) Google Scholar, 3Honkakoski P. Sueyoshi T. Negishi M. Drug-activated nuclear receptors CAR and PXR.Ann. Med. 2003; 35: 172-182Crossref PubMed Scopus (159) Google Scholar–4Carnahan V.E. Redinbo M.R. Structure and function of the human nuclear xenobiotic receptor PXR.Curr. Drug Metab. 2005; 6: 357-367Crossref PubMed Scopus (76) Google Scholar). However, PXR displays a marked species difference in response to PXR ligands; pregnenolone 16α-carbonitrile (PCN) and dexamethasone are the best known activators of rodent PXR but are weak activators of human PXR, whereas drugs such as rifampicin (RIF) and clotrimazole are strong human PXR activators but are weak activators of rodent PXR (5Ma X. Idle J.R. Gonzalez F.J. The pregnane X receptor: from bench to bedside.Expert Opin. Drug Metab. Toxicol. 2008; 4: 895-908Crossref PubMed Scopus (95) Google Scholar). This species-selective ligand specificity has led to the generation of PXR-humanized mouse models (6Ma X. Shah Y. Cheung C. Guo G.L. Feigenbaum L. Krausz K.W. Idle J.R. Gonzalez F.J. The PREgnane X receptor gene-humanized mouse: a model for investigating drug-drug interactions mediated by cytochromes P450 3A.Drug Metab. Dispos. 2007; 35: 194-200Crossref PubMed Scopus (117) Google Scholar, 7Xie W. Barwick J.L. Downes M. Blumberg B. Simon C.M. Nelson M.C. Neuschwander-Tetri B.A. Brunt E.M. Guzelian P.S. Evans R.M. Humanized xenobiotic response in mice expressing nuclear receptor SXR.Nature. 2000; 406: 435-439Crossref PubMed Scopus (611) Google Scholar–8Gong H. Singh S.V. Singh S.P. Mu Y. Lee J.H. Saini S.P. Toma D. Ren S. Kagan V.E. Day B.W. et al.Orphan nuclear receptor pregnane X receptor sensitizes oxidative stress responses in transgenic mice and cancerous cells.Mol. Endocrinol. 2006; 20: 279-290Crossref PubMed Scopus (89) Google Scholar). Subsequent genetic profiling studies have shown that PXR activation regulates the expression of a large network of genes. In genetic profiling for rats treated with the rodent-specific ligand, PCN, hundreds of genes were differentially expressed (9Guzelian J. Barwick J.L. Hunter L. Phang T.L. Quattrochi L.C. Guzelian P.S. Identification of genes controlled by the pregnane X receptor by microarray analysis of mRNAs from pregnenolone 16alpha-carbonitrile-treated rats.Toxicol. Sci. 2006; 94: 379-387Crossref PubMed Scopus (37) Google Scholar). In PXR-humanized mice with constitutively highly expressed human PXR, 146 genes were up- or down-regulated (10Rosenfeld J.M. Vargas Jr., R. Xie W. Evans R.M. Genetic profiling defines the xenobiotic gene network controlled by the nuclear receptor pregnane X receptor.Mol. Endocrinol. 2003; 17: 1268-1282Crossref PubMed Scopus (196) Google Scholar). Among the up-regulated genes by PXR activation, many were known PXR target genes. The most significantly induced are the cytochrome P450s CYP3A and CYP2B subfamilies (11Kliewer S.A. Moore J.T. Wade L. Staudinger J.L. Watson M.A. Jones S.A. McKee D.D. Oliver B.B. Willson T.M. Zetterstrom R.H. et al.An orphan nuclear receptor activated by pregnanes defines a novel steroid signaling pathway.Cell. 1998; 92: 73-82Abstract Full Text Full Text PDF PubMed Scopus (1344) Google Scholar, 12Xie W. Barwick J.L. Simon C.M. Pierce A.M. Safe S. Blumberg B. Guzelian P.S. Evans R.M. Reciprocal activation of xenobiotic response genes by nuclear receptors SXR/PXR and CAR.Genes Dev. 2000; 14: 3014-3023Crossref PubMed Scopus (465) Google Scholar). Conjugating enzymes such as UDP-glucuronosyltransferase (UGT) and glutathione S-transferase and transporters, such as P-glycoprotein, multidrug resistance-related protein-3 (MRP3), and organic anion are induced PXR activation S. M. of by pregnane X receptor Metab. Dispos. 2003; PubMed Scopus Google Scholar, R.H. T. Xie W. A. Regulation of Drug Metab. 2003; 4: PubMed Scopus Google Scholar, Regulation of the glutathione S-transferase gene by of both the and pregnane X Google Scholar, A. M. receptor response elements of by Chem. Full Text Full Text PDF PubMed Scopus Google G.L. Staudinger J. of organic anion 2 by is with pregnane X receptor.Mol. 2002; PubMed Scopus Google Scholar). enzymes and transporters induced by PXR activation the and of xenobiotics and endobiotics. studies have revealed that PXR has a function in hepatic metabolism and an important of the of certain metabolic Activation of PXR hepatic metabolism by hepatic fatty acid and and synthesis Y. Negishi M. S. The of nuclear receptors CAR and PXR in hepatic Metab. 2008; PubMed Scopus Google Scholar). This of by PXR is with such as and activated receptor S. C. Negishi M. Y. receptors CAR and PXR with to genes that and PubMed Scopus Google Scholar, J. S. Y. receptor and hepatic nuclear in hepatic metabolism is mediated by for to the and to the and Chem. 2006; Full Text Full Text PDF PubMed Scopus Google Moore R. Negishi M. Sueyoshi T. pregnane X receptor with to of metabolism in mouse Chem. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar). to the on the of nuclear receptor activation have been the of ultra-performance liquid chromatography (UPLC) coupled with the mass of time-of-flight mass spectrometry In the of genetically modified mouse models has important results that the and of nuclear receptor activation. This combination of mass and genetically modified mice has revealed that activation of activated receptor the metabolism of and fatty acids Y. Krausz K.W. C. Idle J.R. Gonzalez F.J. and genetic analysis of biomarkers for receptor expression and Endocrinol. 2007; PubMed Scopus Google Scholar, J.R. Gonzalez F.J. Metab. 2007; 6: Full Text Full Text PDF PubMed Scopus Google and that novel steroid in can be biomarkers for activation of Y. Krausz K.W. C. Idle J.R. Gonzalez F.J. and genetic analysis of biomarkers for receptor expression and Endocrinol. 2007; PubMed Scopus Google Scholar). In this study, metabolomic responses to PXR activation by PCN in Pxr-null and wild-type mice were investigated coupled with data analysis may be useful to novel biomarkers for activation of PXR and to metabolic by 16α-carbonitrile from and were from was from and were from Pxr-null by A. and and PXR-humanized mice were a with and a The mouse was Pxr-null and PXR-humanized mice were (6Ma X. Shah Y. Cheung C. Guo G.L. Feigenbaum L. Krausz K.W. Idle J.R. Gonzalez F.J. The PREgnane X receptor gene-humanized mouse: a model for investigating drug-drug interactions mediated by cytochromes P450 3A.Drug Metab. Dispos. 2007; 35: 194-200Crossref PubMed Scopus (117) Google Scholar, J.L. B. Jones S.A. D. A. Y. J. et nuclear receptor PXR is a acid that liver Sci. PubMed Scopus Google Scholar). of to were for on and with and the PCN was in and a of and by to wild-type and Pxr-null mice for 4 mice were with were from mice in metabolic for and the last Pxr-null and PXR-humanized mice were with a or for 4 were on the of were the of the study, were the last and liver were and for for studies were by the and and were in with the of of were with 4 of and for to and were with and The were a and The liquid and mass of the was the as Y. Krausz K.W. C. Idle J.R. 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D. R. are in by and Med. PubMed Scopus Google Scholar). is for the of CYP3A M. D. R. are in by and Med. PubMed Scopus Google and P450 of of of vitamin E Chem. 2002; Full Text Full Text PDF PubMed Scopus Google in the mouse to as as may of The and genes to the superfamily K.W. B. C. S. T. for the (UGT) gene 2005; PubMed Scopus Google are likely involved in of with acid or of PCN was in wild-type of and in the mouse was not from the mouse in both wild-type and Pxr-null mice and are genes involved in β-oxidation in Moore R. Negishi M. Sueyoshi T. pregnane X receptor with to of metabolism in mouse Chem. 2007; Full Text Full Text PDF PubMed Scopus Google were not differentially expressed the mouse an involved in peroxisomal of fatty was significantly in the with the in wild-type mice but not in Pxr-null whereas the of an involved in peroxisomal of fatty was not in of the mouse In this study, a combination of metabolomic analysis and genetically modified mouse models was to that activation of PXR results in attenuated vitamin E in of the PXR regulates numerous genes involved in metabolism of xenobiotics and including and and In studies have shown that activation of PXR and Moore R. Negishi M. Sueyoshi T. pregnane X receptor with to of metabolism in mouse Chem. 2007; Full Text Full Text PDF PubMed Scopus Google Scholar, A. P. J.M. CAR and PXR activation and on and 2008; PubMed Scopus Google Scholar). the of vitamin E metabolism by activation of PXR is of of vitamin E by has been M. D. R. are in by and Med. PubMed Scopus Google Scholar). for PXR activation were investigated in both Pxr-null and wild-type mice. Multivariate analysis by revealed the urinary metabolomes PCN were with the PXR activation by PCN, both and Pxr-null mice were whereas and wild-type mice were in the metabolomes that with activation of PXR by PCN in wild-type mice were The most attenuated PXR activation were the vitamin E glucuronide and γ-CEHC Glc. glucuronide and γ-CEHC Glc in were dependent the vitamin E a of vitamin E or vitamin novel endogenous metabolite of γ-CEHC Glc was metabolomic study of PXR activation. The of in mice was γ-CEHC whereas the of was γ-CEHC glucuronide was in a of of the γ-CEHC Glc not be that that in human S.A. and analysis of conjugates of the vitamin E metabolite, Med. 2002; PubMed Scopus Google Scholar). 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The peroxisomal of is by a of including fatty acid and sterol carrier of was significantly by PXR activation, significantly to of in activation of as a peroxisomal in of branched-chain and in the of toxic branched-chain A.M. H. H. et and of sterol carrier Lipid Res. PubMed Scopus Google Scholar). In a mice treated with a of a to branched-chain D. J.T. J. of gene on branched-chain fatty acid J. 2007; PubMed Scopus Google Scholar). of is by the S. J.L. K.W. Regulation of sterol carrier protein gene expression by the Lipid Res. Full Text Full Text PDF PubMed Scopus Google but not Y. M. Y. of protein carrier protein on as a in PubMed Scopus Google Scholar, J.M. of fatty in response to and PubMed Scopus Google Scholar). metabolism was not by an of peroxisomal in M. D. R. are in by and Med. PubMed Scopus Google and urinary CEHC were not in wild-type mice treated with the rodent acid not activation of PXR hepatic by the expression of and peroxisomal β-oxidation by in attenuated levels of glucuronide and γ-CEHC Glc in as shown the metabolic of vitamin E in studies suggested that PXR or receptor activation by gene with PCN the of in wild-type but not in Pxr-null mice in mouse liver Moore R. Negishi M. Sueyoshi T. pregnane X receptor with to of metabolism in mouse Chem. 2007; Full Text Full Text PDF PubMed Scopus Google the expression of in data by PCN in mouse The of is controlled by and such as the nuclear and A. P. J.M. CAR and PXR activation and on and 2008; PubMed Scopus Google Scholar). two be involved in and gene repression by with of gene and the A. P. J.M. CAR and PXR activation and on and 2008; PubMed Scopus Google Scholar). In to activation of PXR and CAR hepatic metabolism by hepatic enzymes such as and PXR activation by with or by from to its in the gene J. S. 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The in have been by a lower metabolism of vitamin E due to PXR activation. However, studies for of vitamin E in liver with PXR activation be metabolomic In the combination of metabolomic analysis and genetically modified mouse a novel vitamin E metabolite, γ-CEHC was activated PXR was to significantly lower the of the glucuronide and γ-CEHC Glc in wild-type but not in Pxr-null mice. Activation of PXR in wild-type mice was to expression of the hepatic PXR activation results in of peroxisomal β-oxidation of including by the expression of the with in both vitamin E and