title: Modulation of tight junction proteins in the perineurium to facilitate peripheral opioid analgesia.
abstract: BACKGROUND
  Peripheral application of opioids reduces inflammatory pain but is less effective in noninflamed tissue of rats and human patients. Hypertonic solutions can facilitate the antinociceptive activity of hydrophilic opioids in noninflamed tissue in vivo. However, the underlying mechanisms are not well understood. We hypothesized that the enhanced efficacy of opioids may be because of opening of the perineurial barrier formed by tight junction-proteins like claudin-1.
  
  
  METHODS
  Male Wistar rats were treated intraplantarly with 10% NaCl. Pain behavior (n = 6) and electrophysiological recordings (n = 9 or more) from skin-nerve preparations after local application of the opioid [d-Ala2,N-Me-Phe4,Gly5-ol]enkephalin (DAMGO) were explored. Tight junction-proteins as well as permeability of the barrier were examined by immunohistochemistry and Western blot (n = 3 or more).
  
  
  RESULTS
  Local administration of 10% NaCl facilitated increased mechanical nociceptive thresholds in response to DAMGO, penetration of horseradish peroxidase into the nerve, as well as a reduced response of C- but not Aδ-nociceptors to mechanical stimulation after application of DAMGO in the skin-nerve preparation. In noninflamed paw tissue, claudin-1 was expressed in the epidermis, blood vessels, and the perineurium, surrounding neurons immunoreactive for calcitonin gene-related peptide or protein gene product 9.5. Claudin-1 but not claudin-5 or occludin was significantly reduced after pretreatment with 10% NaCl. Intraplantar application of a metalloproteinase inhibitor (GM6001) completely reversed these effects.
  
  
  CONCLUSIONS
  Hypertonic saline opens the perineurial barrier via metalloproteinase activation and claudin-1 regulation, thereby allowing access of hydrophilic drugs to peripheral opioid receptors. This principle may be used to specifically target hydrophilic drugs to peripheral neurons.
authors.affiliation: Department of Anesthesiology and Critical Care, University of Wuerzburg, Wuerzburg, Germany. rittner_h@klinik.uni-wuerzburg.de
authors.forename: Heike L
authors.initials: HL
authors.lastname: Rittner
authors.forename: Salah
authors.initials: S
authors.lastname: Amasheh
authors.forename: Rabih
authors.initials: R
authors.lastname: Moshourab
authors.forename: Dagmar
authors.initials: D
authors.lastname: Hackel
authors.forename: Reine-Solange
authors.initials: RS
authors.lastname: Yamdeu
authors.forename: Shaaban A
authors.initials: SA
authors.lastname: Mousa
authors.forename: Michael
authors.initials: M
authors.lastname: Fromm
authors.forename: Christoph
authors.initials: C
authors.lastname: Stein
authors.forename: Alexander
authors.initials: A
authors.lastname: Brack
mesh_terms: D000698:Analgesia; D000701:Analgesics, Opioid / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D062445:Claudin-1; D055724:Electrophysiological Phenomena / Q000187:drug effects; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / Q000008:administration & dosage / Q000494:pharmacology; D005455:Fluorescent Antibody Technique; D005528:Foot; D007267:Injections; D008297:Male; D008565:Membrane Proteins / Q000378:metabolism; D045726:Metalloproteases / Q000378:metabolism; D018613:Microscopy, Confocal; D009413:Nerve Fibers, Myelinated / Q000187:drug effects; D036421:Nerve Fibers, Unmyelinated / Q000187:drug effects; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009619:Nociceptors / Q000187:drug effects; D062793:Occludin; D017288:Pain Threshold / Q000187:drug effects; D010525:Peripheral Nerves / Q000187:drug effects / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012462:Saline Solution, Hypertonic / Q000494:pharmacology; D019108:Tight Junctions / Q000187:drug effects*
chemical_list: D000701:Analgesics, Opioid; C568108:CLDN1 protein, human; D062445:Claudin-1; C568114:Cldn1 protein, rat; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; C568985:OCLN protein, human; D062793:Occludin; C568987:Ocln protein, rat; D012462:Saline Solution, Hypertonic; D020875:Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; D045726:Metalloproteases