title: Discovery that theonellasterol a marine sponge sterol is a highly selective FXR antagonist that protects against liver injury in cholestasis.
abstract: BACKGROUND
  The farnesoid-x-receptor (FXR) is a bile acid sensor expressed in the liver and gastrointestinal tract. Despite FXR ligands are under investigation for treatment of cholestasis, a biochemical condition occurring in a number of liver diseases for which available therapies are poorly effective, mice harboring a disrupted FXR are protected against liver injury caused by bile acid overload in rodent models of cholestasis. Theonellasterol is a 4-methylene-24-ethylsteroid isolated from the marine sponge Theonella swinhoei. Here, we have characterized the activity of this theonellasterol on FXR-regulated genes and biological functions.
  
  
  RESULTS
  Interrogation of HepG2 cells, a human hepatocyte cell line, by microarray analysis and transactivation assay shows that theonellasterol is a selective FXR antagonist, devoid of any agonistic or antagonistic activity on a number of human nuclear receptors including the vitamin D receptor, PPARs, PXR, LXRs, progesterone, estrogen, glucorticoid and thyroid receptors, among others. Exposure of HepG2 cells to theonellasterol antagonizes the effect of natural and synthetic FXR agonists on FXR-regulated genes, including SHP, OSTα, BSEP and MRP4. A proof-of-concept study carried out to investigate whether FXR antagonism rescues mice from liver injury caused by the ligation of the common bile duct, a model of obstructive cholestasis, demonstrated that theonellasterol attenuates injury caused by bile duct ligation as measured by assessing serum alanine aminostrasferase levels and extent of liver necrosis at histopathology. Analysis of genes involved in bile acid uptake and excretion by hepatocytes revealed that theonellasterol increases the liver expression of MRP4, a basolateral transporter that is negatively regulated by FXR. Administering bile duct ligated mice with an FXR agonist failed to rescue from liver injury and downregulated the expression of MRP4.
  
  
  CONCLUSIONS
  FXR antagonism in vivo results in a positive modulation of MRP4 expression in the liver and is a feasible strategy to target obstructive cholestasis.
authors.affiliation: Dipartimento di Medicina Clinica e Sperimentale, Nuova Facoltà di Medicina e Chirurgia, Università di Perugia, S. Andrea delle Fratte, Perugia, Italy.
authors.forename: Barbara
authors.initials: B
authors.lastname: Renga
authors.forename: Andrea
authors.initials: A
authors.lastname: Mencarelli
authors.forename: Claudio
authors.initials: C
authors.lastname: D'Amore
authors.forename: Sabrina
authors.initials: S
authors.lastname: Cipriani
authors.forename: Maria Valeria
authors.initials: MV
authors.lastname: D'Auria
authors.forename: Valentina
authors.initials: V
authors.lastname: Sepe
authors.forename: Maria Giovanna
authors.initials: MG
authors.lastname: Chini
authors.forename: Maria Chiara
authors.initials: MC
authors.lastname: Monti
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Bifulco
authors.forename: Angela
authors.initials: A
authors.lastname: Zampella
authors.forename: Stefano
authors.initials: S
authors.lastname: Fiorucci
mesh_terms: D000818:Animals; D059001:Aquatic Organisms / Q000737:chemistry; D002780:Cholestasis, Intrahepatic / Q000188:drug therapy* / Q000473:pathology; D019610:Cytoprotection / Q000187:drug effects; D004195:Disease Models, Animal; D055808:Drug Discovery; D004353:Drug Evaluation, Preclinical; D005240:Feasibility Studies; D056945:Hep G2 Cells; D006727:Hormone Antagonists / Q000302:isolation & purification / Q000494:pharmacology / Q000627:therapeutic use; D006801:Humans; D008099:Liver / Q000187:drug effects / Q000293:injuries / Q000473:pathology; D051379:Mice; D011161:Porifera / Q000737:chemistry; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors*; D013261:Sterols / Q000302:isolation & purification / Q000494:pharmacology* / Q000627:therapeutic use*; D013379:Substrate Specificity; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D006727:Hormone Antagonists; D018160:Receptors, Cytoplasmic and Nuclear; D013261:Sterols; D000099150:Receptor, Farnesoid X-Activated; C412852:7-hydroxytheonellasterol