title: Inhibition of firefly luciferase by general anesthetics: effect on in vitro and in vivo bioluminescence imaging.
abstract: Bioluminescence imaging is routinely performed in anesthetized mice. Often isoflurane anesthesia is used because of its ease of use and fast induction/recovery. However, general anesthetics have been described as important inhibitors of the luciferase enzyme reaction.
  
  
  OBJECTIVE
  To investigate frequently used mouse anesthetics for their direct effect on the luciferase reaction, both in vitro and in vivo.
  
  
  METHODS
  isoflurane, sevoflurane, desflurane, ketamine, xylazine, medetomidine, pentobarbital and avertin were tested in vitro on luciferase-expressing intact cells, and for non-volatile anesthetics on intact cells and cell lysates. In vivo, isoflurane was compared to unanesthetized animals and different anesthetics. Differences in maximal photon emission and time-to-peak photon emission were analyzed.
  
  
  RESULTS
  All volatile anesthetics showed a clear inhibitory effect on the luciferase activity of 50% at physiological concentrations. Avertin had a stronger inhibitory effect of 80%. For ketamine and xylazine, increased photon emission was observed in intact cells, but this was not present in cell lysate assays, and was most likely due to cell toxicity and increased cell membrane permeability. In vivo, the highest signal intensities were measured in unanesthetized mice and pentobarbital anesthetized mice, followed by avertin. Isoflurane and ketamine/medetomidine anesthetized mice showed the lowest photon emission (40% of unanesthetized), with significantly longer time-to-peak than unanesthetized, pentobarbital or avertin-anesthetized mice. We conclude that, although strong inhibitory effects of anesthetics are present in vitro, their effect on in vivo BLI quantification is mainly due to their hemodynamic effects on mice and only to a lesser extent due to the direct inhibitory effect.
authors.affiliation: In Vivo Cellular and Molecular Imaging (ICMI) Laboratory, Vrije Universiteit Brussel (VUB), Brussels, Belgium. mkeyaerts@gmail.com
authors.forename: Marleen
authors.initials: M
authors.lastname: Keyaerts
authors.forename: Isabel
authors.initials: I
authors.lastname: Remory
authors.forename: Vicky
authors.initials: V
authors.lastname: Caveliers
authors.forename: Karine
authors.initials: K
authors.lastname: Breckpot
authors.forename: Tomas J
authors.initials: TJ
authors.lastname: Bos
authors.forename: Jan
authors.initials: J
authors.lastname: Poelaert
authors.forename: Axel
authors.initials: A
authors.lastname: Bossuyt
authors.forename: Tony
authors.initials: T
authors.lastname: Lahoutte
mesh_terms: D000758:Anesthesia; D018681:Anesthetics, General / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D019540:Area Under Curve; D002457:Cell Extracts; D002460:Cell Line; D004791:Enzyme Inhibitors / Q000008:administration & dosage / Q000494:pharmacology*; D000431:Ethanol / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000494:pharmacology; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007267:Injections; D007649:Ketamine / Q000008:administration & dosage / Q000494:pharmacology; D049409:Luciferases, Firefly / Q000037:antagonists & inhibitors* / Q000378:metabolism; D008163:Luminescent Measurements / Q000379:methods*; D008297:Male; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology; D051379:Mice; D008819:Mice, Nude; D010424:Pentobarbital / Q000008:administration & dosage / Q000494:pharmacology; D017785:Photons; D014835:Volatilization / Q000187:drug effects; D014991:Xylazine / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D018681:Anesthetics, General; D002457:Cell Extracts; D004791:Enzyme Inhibitors; C062527:tribromoethanol; D014991:Xylazine; D000431:Ethanol; D007649:Ketamine; D049409:Luciferases, Firefly; D010424:Pentobarbital; D020926:Medetomidine