Identification of CYP3A4 as the major enzyme responsible for 25-hydroxylation of 5β-cholestane-3α,7α,12α-triol in human liver microsomes

Furster, Catrin; Wikvall, Kjell

doi:10.1016/s0005-2760(98)00175-1

Cited by 47 publications

(43 citation statements)

References 20 publications

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“…1). Other groups have recently demonstrated that the enzymatic activity of CYP3A11, which serves as a 5␤-cholestan-3␣,7␣,12␣-triol hydroxylase, is markedly up-regulated in the livers of Cyp27a1 Ϫ/Ϫ mice (7,21).…”

Section: Resultsmentioning

confidence: 99%

“…Future studies on the substrate specificity of these metabolites by CYP3A or other PXR target gene products should address this issue. Because human CYP3A4 can also catalyze the hydroxylation of bile acid precursors (21), potent human PXR agonists that increase CYP3A4 activity may prove useful in the treatment of disease in which a toxic accumulation of bile acid intermediates occurs.…”

Section: Figmentioning

confidence: 99%

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Identification of bile acid precursors as endogenous ligands for the nuclear xenobiotic pregnane X receptor

Goodwin

Gauthier

Umetani

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

178

128

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Sterol 27-hydroxylase (CYP27A1) is required for bile acid synthesis by both the classical and alternate pathways. Cyp27a1 ؊/؊ mice exhibit a dramatic increase in the activity of cytochrome P450 3A (CYP3A), which catalyzes side-chain hydroxylations of bile acid intermediates, thereby facilitating their excretion in the bile and urine. We examine the role of the nuclear xenobiotic receptor PXR (pregnane X receptor) in this process. We demonstrate that expression of Cyp3a11 and other established PXR target genes is increased in the Cyp27a1 ؊/؊ mice. WhenCyp27a1 ؊/؊ mice are fed a diet containing either cholic acid or chenodeoxycholic acid, expression of CYP7A1, which catalyzes the rate-limiting step in bile acid biosynthesis, is strongly suppressed. In parallel, the induction of Cyp3a11 observed in these mice is reversed, suggesting that bile acid intermediates serve as PXR activators. In support of this hypothesis, three potentially toxic sterols (7␣-hydroxy-4-cholesten-3-one, 5␤-cholestan-3␣,7␣,12␣-triol, and 4-cholesten-3-one), including two that are known to accumulate in Cyp27a1 ؊/؊ mice, are efficacious activators of mouse PXR. All three compounds are more potent activators of mouse PXR than of human PXR, which may explain in part why humans who lack functional CYP27A1 do not display a corresponding increase in CYP3A activity and are stricken with the disease cerebrotendinous xanthomatosis. Taken together, these results reveal the existence of a feedforward regulatory loop by which potentially toxic bile acid intermediates activate PXR and induce their own metabolism. In addition, this study demonstrates that animal models with alterations in gene expression can be used to identify endogenous ligands for orphan nuclear receptors.

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Section: Resultsmentioning

confidence: 99%

Section: Figmentioning

confidence: 99%

Identification of bile acid precursors as endogenous ligands for the nuclear xenobiotic pregnane X receptor

Goodwin

Gauthier

Umetani

et al. 2002

Proc. Natl. Acad. Sci. U.S.A.

178

128

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“…-13 -Among the drug-metabolizing CYPs, CYP3As are the major class of enzymes that hydroxylate bile acids [51,90,91]. Moreover, transcriptional induction of CYP3A genes by bile acids often exceeds that of CYP2B and CYP2C genes (refs.…”

Section: Nuclear Receptor Regulation Of Cholesterol Biosynthesis and mentioning

confidence: 99%

“…cholestasis), the xenosensors are activated by these elevated bile acid levels and subsequently promote alternate mechanisms in order to lower intrahepatic bile acid levels before they become hepatotoxic. In summary, the four nuclear receptors FXR, PXR, CAR, and VDR are functionally related inasmuch as they coordinately reduce hepatic bile acid levels by increasing bile acid metabolism and export and in part by inhibiting de novo biosynthesis of bile acids from cholesterol [89].-13 -Among the drug-metabolizing CYPs, CYP3As are the major class of enzymes that hydroxylate bile acids [51,90,91]. Moreover, transcriptional induction of CYP3A genes by bile acids often exceeds that of CYP2B and CYP2C genes (refs.…”

mentioning

confidence: 99%

Regulatory network of lipid-sensing nuclear receptors: roles for CAR, PXR, LXR, and FXR

Handschin¹,

Meyer²

2005

Archives of Biochemistry and Biophysics

156

105

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Cloning and characterization of the orphan nuclear receptors constitutive androstane receptor (CAR, NR1I3) and pregnane X receptor (PXR, NR1I2) led to major breakthroughs in studying drug-mediated transcriptional induction of drugmetabolizing cytochromes P450 (CYP). More recently, additional roles for CAR and PXR have been discovered. As examples, these xenosensors are involved in the homeostasis of cholesterol, bile acids, bilirubin and other endogenous hydrophobic molecules in the liver: CAR and PXR thus form an intricate regulatory network with other members of the nuclear receptor superfamily, foremost the cholesterol-sensing liver X receptor (LXR, NR1H2/3) and the bileacid-activated farnesoid X receptor (FXR, NR1H4). In this review, functional interactions between these nuclear receptors as well as the consequences on physiology and pathophysiology of the liver are discussed.Key Words: nuclear receptors; drug-induction; lipids; bile acids; cholesterol; CAR; PXR; LXR; FXR; cytochrome P450 -4 -Metabolism of drugs and other xenobiotics in the liver is our body's primary defense against accumulation of potentially toxic, lipophilic compounds. The superfamily of cytochromes P450 (CYPs) are the best-studied class of enzymes in this task [1]. Transcriptional and post-transcriptional regulation of CYPs after exposure to certain drugs or other xenobiotics has been described several decades ago. Classically, the barbiturate phenobarbital induces its own metabolism and excretion by elevating CYP levels [2]. However, the molecular mechanisms underlying this observation remained a conundrum until the discovery and subsequent characterization of the constitutive androstane receptor (CAR, official nomenclature NR1I3) and the pregnane X receptor (PXR, NR1I2, alternatively called PAR or SXR), two members of the superfamily of nuclear receptors [3][4][5][6][7]. Mice with genetic ablations of CAR and PXR have significantly reduced inducibility of CYPs by a variety of drugs [8,9]. Whereas these two receptors share some common ligands and also have an overlapping target gene pattern [10][11][12][13], the mode of activation for CAR and PXR is quite different [14]. PXR is located in the nucleus, it has a low basal activity and is highly activated upon ligand binding [14,15]. In contrast, in the non-induced state, CAR resides in the cytoplasm. After treatment with activators such as phenobarbital, CAR shuttles to the nucleus to activate its target genes. Moreover, CAR localization and activity is regulated by various protein phosphorylation events [16][17][18]. For a more detailed discussion of CAR and PXR functions in drug-mediated induction of CYPs, see some recent reviews (e.g. refs. [19-23] and references therein).-5 - The nuclear receptor NR1I group includes xenosensors and lipid-sensing membersCompounds that induce transcription of CYPs and that activate CAR and PXR are structurally very diverse [21]. However, most of them are small in size and are highly lipophilic [24]. Whereas the CAR ligand-binding domain stru...

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“…Previous studies have demonstrated that the cholesterol metabolite 5␤-cholestane-3␣,7␣,12␣-triol (triol) is an endogenous CYP3A substrate (10,11). Although CYP3A can metabolize triol, the predominant route of triol metabolism is catalyzed by CYP27 (sterol-27-hydroxylase).…”

mentioning

confidence: 99%

Identification of an endogenous ligand that activates pregnane X receptor-mediated sterol clearance

Dussault

Yoo

Lin

et al. 2003

Proc. Natl. Acad. Sci. U.S.A.

113

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The nuclear receptor PXR (pregnane X receptor) is a broadspecificity sensor that recognizes a wide variety of synthetic drugs and xenobiotic agents. On activation by these compounds, PXR coordinately induces a network of transporters, cytochrome P450 enzymes, and other genes that effectively clear xenobiotics from the liver and intestine. Like PXR, the majority of its target genes also possess a broad specificity for exogenous compounds. Thus, PXR is both a sensor and effector in a well integrated and generalized pathway for chemical immunity. Although it is clear that PXR responds to numerous foreign compounds, it is unclear whether it possesses an endogenous ligand. To address this issue, we noted that there is substantial overlap in the substrate specificities of PXR and its critical CYP3A target gene. This prompted us to ask whether endogenous CYP3A substrates also serve as PXR ligands. We demonstrate that 5␤-cholestane-3␣,7␣,12␣-triol (triol), a cholesterol-derived CYP3A substrate, is a potent PXR agonist that effectively induces cyp3a expression in mice. This defines a critical salvage pathway that can be autoinduced to minimize triol accumulation. In contrast, triol can accumulate to very high levels in humans, and unlike mice, these people develop the severe clinical manifestations of cerebrotendinous xanthomatosis. The reason for these dramatic species differences has remained unclear. We now demonstrate that triol fails to activate human PXR or induce the CYP3A-salvage pathway. This explains why humans are more susceptible to sterol accumulation and suggests that synthetic ligands for human PXR could be used to treat cerebrotendinous xanthomatosis and other disorders of cholesterol excess.

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Identification of CYP3A4 as the major enzyme responsible for 25-hydroxylation of 5β-cholestane-3α,7α,12α-triol in human liver microsomes

Cited by 47 publications

References 20 publications

Identification of bile acid precursors as endogenous ligands for the nuclear xenobiotic pregnane X receptor

Identification of bile acid precursors as endogenous ligands for the nuclear xenobiotic pregnane X receptor

Regulatory network of lipid-sensing nuclear receptors: roles for CAR, PXR, LXR, and FXR

Identification of an endogenous ligand that activates pregnane X receptor-mediated sterol clearance

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