title: CETP inhibitors downregulate hepatic LDL receptor and PCSK9 expression in vitro and in vivo through a SREBP2 dependent mechanism.
abstract: BACKGROUND
  CETP inhibitors block the transfer of cholesteryl ester from HDL-C to VLDL-C and LDL-C, thereby raising HDL-C and lowering LDL-C. In this study, we explored the effect of CETP inhibitors on hepatic LDL receptor (LDLR) and PCSK9 expression and further elucidated the underlying regulatory mechanism.
  
  
  RESULTS
  We first examined the effect of anacetrapib (ANA) and dalcetrapib (DAL) on LDLR and PCSK9 expression in hepatic cells in vitro. ANA exhibited a dose-dependent inhibition on both LDLR and PCSK9 expression in CETP-positive HepG2 cells and human primary hepatocytes as well as CETP-negative mouse primary hepatocytes (MPH). Moreover, the induction of LDLR protein expression by rosuvastatin in MPH was blunted by cotreatment with ANA. In both HepG2 and MPH ANA treatment reduced the amount of mature form of SREBP2 (SREBP2-M). In vivo, oral administration of ANA to dyslipidemic C57BL/6J mice at a daily dose of 50 mg/kg for 1 week elevated serum total cholesterol by approximately 24.5% (p < 0.05%) and VLDL-C by 70% (p < 0.05%) with concomitant reductions of serum PCSK9 and liver LDLR/SREBP2-M protein. Finally, we examined the in vitro effect of two other strong CETP inhibitors evacetrapib and torcetrapib on LDLR/PCSK9 expression and observed a similar inhibitory effect as ANA in a concentration range of 1-10 μM.
  
  
  CONCLUSIONS
  Our study revealed an unexpected off-target effect of CETP inhibitors that reduce the mature form of SREBP2, leading to attenuated transcription of hepatic LDLR and PCSK9. This negative regulation of SREBP pathway by ANA manifested in mice where CETP activity was absent and affected serum cholesterol metabolism.
authors.affiliation: Department of Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
authors.forename: Bin
authors.initials: B
authors.lastname: Dong
authors.affiliation: Department of Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
authors.forename: Amar Bahadur
authors.initials: AB
authors.lastname: Singh
authors.affiliation: Department of Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
authors.forename: Chin
authors.initials: C
authors.lastname: Fung
authors.affiliation: Department of Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA.
authors.forename: Kelvin
authors.initials: K
authors.lastname: Kan
authors.affiliation: Department of Veterans Affairs Palo Alto Health Care System, 3801 Miranda Avenue, Palo Alto, CA 94304, USA. Electronic address: Jingwen.Liu@va.gov.
authors.forename: Jingwen
authors.initials: J
authors.lastname: Liu
mesh_terms: D000577:Amides; D000818:Animals; D000924:Anticholesteremic Agents / Q000494:pharmacology*; D002784:Cholesterol / Q000378:metabolism*; D053480:Cholesterol Ester Transfer Proteins / Q000037:antagonists & inhibitors*; D015536:Down-Regulation; D050171:Dyslipidemias / Q000097:blood; D004952:Esters; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000378:metabolism; D006801:Humans; D008055:Lipids / Q000097:blood; D008297:Male; D023303:Oxazolidinones / Q000494:pharmacology; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases / Q000096:biosynthesis*; D011973:Receptors, LDL / Q000096:biosynthesis*; D012697:Serine Endopeptidases / Q000096:biosynthesis*; D051782:Sterol Regulatory Element Binding Protein 2 / Q000502:physiology*; D013438:Sulfhydryl Compounds / Q000494:pharmacology
chemical_list: D000577:Amides; D000924:Anticholesteremic Agents; D053480:Cholesterol Ester Transfer Proteins; D004952:Esters; D008055:Lipids; D023303:Oxazolidinones; D011973:Receptors, LDL; D051782:Sterol Regulatory Element Binding Protein 2; D013438:Sulfhydryl Compounds; C411602:dalcetrapib; D002784:Cholesterol; C472125:PCSK9 protein, human; D000071449:Proprotein Convertase 9; D043484:Proprotein Convertases; D012697:Serine Endopeptidases; C530884:anacetrapib
keywords: CETP inhibitors; Hyperlipidemia; LDL receptor; PCSK9; SREBP2