title: Rapamycin impairs endothelial cell function in human internal thoracic arteries.
abstract: BACKGROUND
  Definitive fate of the coronary endothelium after implantation of a drug-eluting stent remains unclear, but evidence has accumulated that treatment with rapamycin-eluting stents impairs endothelial function in human coronary arteries. The aim of our study was to demonstrate this phenomenon on functional, morphological and biochemical level in human internal thoracic arteries (ITA) serving as coronary artery model.
  
  
  METHODS
  After exposure to rapamycin for 20 h, functional activity of ITA rings was investigated using the organ bath technique. Morphological analysis was performed by scanning electron microscopy and evaluated by two independent observers in blinded fashion. For measurement of endothelial nitric oxide synthase (eNOS) release, mammalian target of rapamycin (mTOR) and protein kinase B (PKB) (Akt) activation, Western blotting on human mammary epithelial cells-1 and on ITA homogenates was performed.
  
  
  RESULTS
  Comparison of the acetylcholine-induced relaxation revealed a significant concentration-dependent decrease to 66 ± 7 % and 36 ± 7 % (mean ± SEM) after 20-h incubation with 1 and 10 μM rapamycin. Electron microscopic evaluation of the endothelial layer showed no differences between controls and samples exposed to 10 μM rapamycin. Western blots after 20-h incubation with rapamycin (10 nM-1 μM) revealed a significant and concentration-dependent reduction of p (Ser 1177)-eNOS (down to 38 ± 8 %) in human mammary epithelial cells (Hmec)-1. Furthermore, 1 μM rapamycin significantly reduced activation of p (Ser2481)-mTOR (58 ± 11 %), p (Ser2481)-mTOR (23 ± 4 %) and p (Ser473)-Akt (38 ± 6 %) in ITA homogenates leaving Akt protein levels unchanged.
  
  
  CONCLUSIONS
  The present data suggests that 20-h exposure of ITA rings to rapamycin reduces endothelium-mediated relaxation through down-regulation of Akt-phosphorylation via the mTOR signalling axis within the ITA tissue without injuring the endothelial cell layer.
authors.affiliation: Department of Cardiovascular Surgery, University Hospital Berne, Bern, CH-3010, Switzerland.
authors.forename: David C
authors.initials: DC
authors.lastname: Reineke
authors.affiliation: Department of Cardiac Surgery, University Hospital Basel, Spitalstrasse 21, Basel, CH-4031, Switzerland.|Department of Biomedicine, University Basel, Basel, CH-4031, Switzerland.
authors.forename: Else
authors.initials: E
authors.lastname: Müller-Schweinitzer
authors.affiliation: Department of Cardiovascular Surgery, University Hospital Berne, Bern, CH-3010, Switzerland.|Department of Biomedicine, University Basel, Basel, CH-4031, Switzerland.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Winkler
authors.affiliation: Department of Cardiac Surgery, University Hospital Basel, Spitalstrasse 21, Basel, CH-4031, Switzerland.|Department of Biomedicine, University Basel, Basel, CH-4031, Switzerland.
authors.forename: Donatina
authors.initials: D
authors.lastname: Kunz
authors.affiliation: Department of Anatomy, Johannes Gutenberg-University, Mainz, 55099, Germany.
authors.forename: Moritz A
authors.initials: MA
authors.lastname: Konerding
authors.affiliation: Department of Cardiac Surgery, University Hospital Basel, Spitalstrasse 21, Basel, CH-4031, Switzerland.|Department of Biomedicine, University Basel, Basel, CH-4031, Switzerland.
authors.forename: Thomas
authors.initials: T
authors.lastname: Grussenmeyer
authors.affiliation: Department of Cardiovascular Surgery, University Hospital Berne, Bern, CH-3010, Switzerland.
authors.forename: Thierry P
authors.initials: TP
authors.lastname: Carrel
authors.affiliation: Department of Cardiac Surgery, University Hospital Basel, Spitalstrasse 21, Basel, CH-4031, Switzerland.|Department of Biomedicine, University Basel, Basel, CH-4031, Switzerland.
authors.forename: Friedrich S
authors.initials: FS
authors.lastname: Eckstein
authors.affiliation: Department of Cardiac Surgery, University Hospital Basel, Spitalstrasse 21, Basel, CH-4031, Switzerland. martin.grapow@usb.ch.|Department of Biomedicine, University Basel, Basel, CH-4031, Switzerland. martin.grapow@usb.ch.
authors.forename: Martin T R
authors.initials: MT
authors.lastname: Grapow
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000900:Anti-Bacterial Agents / Q000009:adverse effects / Q000494:pharmacology*; D042783:Endothelial Cells / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D004730:Endothelium, Vascular / Q000187:drug effects* / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D052250:Nitric Oxide Synthase Type III / Q000235:genetics / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D020123:Sirolimus / Q000009:adverse effects / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism; D013895:Thoracic Arteries / Q000166:cytology / Q000187:drug effects*
chemical_list: D000900:Anti-Bacterial Agents; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus