title: Interruption of spinal cord microglial signaling by alpha-2 agonist dexmedetomidine in a murine model of delayed paraplegia.
abstract: BACKGROUND
  Despite investigation into preventable pharmacologic adjuncts, paraplegia continues to complicate thoracoabdominal aortic interventions. The alpha 2a adrenergic receptor agonist, dexmedetomidine, has been shown to preserve neurologic function and neuronal viability in a murine model of spinal cord ischemia reperfusion, although the mechanism remains elusive. We hypothesize that dexmedetomidine will blunt postischemic inflammation in vivo following thoracic aortic occlusion with in vitro demonstration of microglial inhibition following lipopolysaccharide (LPS) stimulation.
  
  
  METHODS
  Adult male C57BL/6 mice underwent 4 minutes of aortic occlusion. Mice received 25 μg/kg intraperitoneal dexmedetomidine (n = 8) or 0.9% normal saline (n = 7) at reperfusion and 12-hour intervals postoperatively until 48 hours. Additionally, sham mice (n = 3), which had aortic arch exposed with no occlusion, were included for comparison. Functional scoring was done at 6 hours following surgery and 12-hour intervals until 60 hours when spinal cords were removed and examined for neuronal viability and cytokine production. Additional analysis of microglia activation was done in 12 hours following surgery. Age- and sex-matched mice had spinal cord removed for microglial isolation culture. Cells were grown to confluence and stimulated with toll-like receptor-4 agonist LPS 100 ng/mL in presence of dexmedetomidine or vehicle control for 24 hours. Microglia and media were then removed for analysis of protein expression.
  
  
  RESULTS
  Dexmedetomidine treatment at reperfusion significantly preserved neurologic function with mice in treatment group having a Basso Score of 6.3 in comparison to 2.3 in ischemic control group. Treatment was associated with a significant reduction in microglia activation and in interleukin-6 production. Microglial cells in isolation when stimulated with LPS had an increased production of proinflammatory cytokines and markers of activation. Treatment with dexmedetomidine significantly attenuated microglial activation and proinflammatory cytokine production in vitro with a greater than twofold reduction in tumor necrosis factor-α.
  
  
  CONCLUSIONS
  Alpha 2a agonist, dexmedetomidine treatment at reperfusion preserved neurologic function and neuronal viability. Furthermore, dexmedetomidine treatment resulted in an attenuation of microglial activation and proinflammatory cytokine production both in vivo and in vitro following LPS stimulation. This finding lends insight into the mechanism of paralysis following thoracic aortic interventions and may guide future pharmacologic targets for attenuating spinal cord ischemia and reperfusion.
authors.affiliation: Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado, Denver, Colo. Electronic address: marshall.bell@ucdenver.edu.
authors.forename: Marshall T
authors.initials: MT
authors.lastname: Bell
authors.affiliation: Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado, Denver, Colo.
authors.forename: Viktor A
authors.initials: VA
authors.lastname: Agoston
authors.affiliation: Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado, Denver, Colo.
authors.forename: Kirsten A
authors.initials: KA
authors.lastname: Freeman
authors.affiliation: Department of Anesthesiology, University of Colorado, Denver, Colo.
authors.forename: Ferenc
authors.initials: F
authors.lastname: Puskas
authors.affiliation: Department of Anesthesiology, University of Colorado, Denver, Colo.
authors.forename: Paco S
authors.initials: PS
authors.lastname: Herson
authors.affiliation: Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado, Denver, Colo.
authors.forename: Joshua
authors.initials: J
authors.lastname: Mares
authors.affiliation: Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado, Denver, Colo.
authors.forename: David A
authors.initials: DA
authors.lastname: Fullerton
authors.affiliation: Department of Surgery, Division of Cardiothoracic Surgery, University of Colorado, Denver, Colo.
authors.forename: T Brett
authors.initials: TB
authors.lastname: Reece
mesh_terms: D058647:Adrenergic alpha-2 Receptor Agonists / Q000494:pharmacology*; D000818:Animals; D000893:Anti-Inflammatory Agents / Q000494:pharmacology; D001013:Aorta, Thoracic / Q000601:surgery; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism; D020927:Dexmedetomidine / Q000494:pharmacology*; D004195:Disease Models, Animal; D018836:Inflammation Mediators / Q000378:metabolism; D008026:Ligation; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D018696:Neuroprotective Agents / Q000494:pharmacology*; D010264:Paraplegia / Q000188:drug therapy* / Q000378:metabolism / Q000503:physiopathology; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects*; D013116:Spinal Cord / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D013997:Time Factors; D051197:Toll-Like Receptor 4 / Q000819:agonists / Q000378:metabolism
chemical_list: D058647:Adrenergic alpha-2 Receptor Agonists; D000893:Anti-Inflammatory Agents; D016207:Cytokines; D018836:Inflammation Mediators; D008070:Lipopolysaccharides; D018696:Neuroprotective Agents; D018341:Receptors, Adrenergic, alpha-2; C493487:Tlr4 protein, mouse; D051197:Toll-Like Receptor 4; D020927:Dexmedetomidine