title: Guggulsterone antagonizes farnesoid X receptor induction of bile salt export pump but activates pregnane X receptor to inhibit cholesterol 7alpha-hydroxylase gene.
abstract: Bile acids activate a nuclear receptor, farnesoid X receptor (FXR), that induces bile salt export pump (BSEP) but inhibits cholesterol 7alpha-hydroxylase (CYP7A1) gene transcription in the liver. Guggulsterone, a plant sterol that lowers serum cholesterol, has been shown to antagonize FXR activated genes. Transient transfection assay of a human BSEP/luciferase reporter in HepG2 cells transfected with FXR reveals that guggulsterone strongly antagonizes bile acid induction of the BSEP gene. On the other hand, guggulsterone has no effect on FXR inhibition of the CYP7A1 gene, but strongly inhibits the human CYP7A1 gene by activation of pregnane X receptor (PXR). These results suggest that guggulsterone inhibits bile acid secretion from hepatocytes into bile and activates PXR to inhibit bile acid synthesis in the liver. Reduced conversion of cholesterol and bile acid excretion may lead to an increase of hepatic cholesterol and decrease of intestinal cholesterol absorption, and results in lowering serum cholesterol.
authors.affiliation: Department of Biochemistry and Molecular Pathology, Northeastern Ohio Univ's College of Medicine, Rootstown, OH 44272, USA.
authors.forename: Erika
authors.initials: E
authors.lastname: Owsley
authors.forename: John Y L
authors.initials: JY
authors.lastname: Chiang
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000235:genetics*; D002460:Cell Line; D002635:Chenodeoxycholic Acid / Q000037:antagonists & inhibitors; D002790:Cholesterol 7-alpha-Hydroxylase / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D000077297:Pregnane X Receptor; D011282:Pregnenediones / Q000494:pharmacology*; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D011987:Receptors, Steroid / Q000378:metabolism*; D014157:Transcription Factors / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015533:Transcriptional Activation / Q000187:drug effects; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D002635:Chenodeoxycholic Acid; D002790:Cholesterol 7-alpha-Hydroxylase; D004268:DNA-Binding Proteins; D000077297:Pregnane X Receptor; D011282:Pregnenediones; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C093491:ABCB11 protein, human; C023617:pregna-4,17-diene-3,16-dione