Attenuation of vascular permeability by methylnaltrexone: role of mOP-R and S1P3 transactivation

Am J Respir Cell Mol Biol. 2007 Aug;37(2):222-31. doi: 10.1165/rcmb.2006-0327OC. Epub 2007 Mar 29.


Endothelial cell (EC) barrier dysfunction (i.e., increased vascular permeability) is observed in inflammatory states, tumor angiogenesis, atherosclerosis, and both sepsis and acute lung injury. Therefore, agents that preserve vascular integrity have important clinical therapeutic implications. We examined the effects of methylnaltrexone (MNTX), a mu opioid receptor (mOP-R) antagonist, on human pulmonary EC barrier disruption produced by edemagenic agents including morphine, the endogenous mOP-R agonist DAMGO, thrombin, and LPS. Pretreatment of EC with MNTX (0.1 muM, 1 h) or the uncharged mOP-R antagonist naloxone attenuated morphine- and DAMGO-induced barrier disruption in vitro. However, MNTX, but not naloxone, pretreatment of EC inhibited thrombin- and LPS-induced barrier disruption, indicating potential mOP-R-independent effects of MNTX. In addition, intravenously delivered MNTX attenuated LPS-induced vascular hyperpermeability in the murine lung. We next examined the mechanistic basis for this MNTX barrier protection and observed that silencing of mOP-R attenuated the morphine- and DAMGO-induced EC barrier disruption, but not the permeability response to either thrombin or LPS. Because activation of the sphingosine 1-phosphate receptor, S1P(3), is key to a number of barrier-disruptive responses, we examined the role of this receptor in the permeability response to mOP-R ligation. Morphine, DAMGO, thrombin, and LPS induced RhoA/ROCK-mediated threonine phosphorylation of S1P(3), which was blocked by MNTX, suggesting S1P(3) transactivation. In addition, silencing of S1P(3) receptor expression (siRNA) abolished the permeability response to each edemagenic agonist. These results indicate that MNTX provides barrier protection against edemagenic agonists via inhibition of S1P(3) receptor activation and represents a potentially useful therapeutic agent for syndromes of increased vascular permeability.

MeSH terms

  • Analgesics, Opioid / metabolism
  • Animals
  • Capillary Permeability / drug effects*
  • Cells, Cultured
  • Electrophysiology
  • Endothelial Cells / cytology
  • Endothelial Cells / drug effects*
  • Endothelial Cells / metabolism
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)- / metabolism
  • Humans
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Molecular Sequence Data
  • Morphine / metabolism
  • Naloxone / metabolism
  • Naltrexone / analogs & derivatives*
  • Naltrexone / pharmacology
  • Narcotic Antagonists / pharmacology*
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism
  • Quaternary Ammonium Compounds / pharmacology
  • RNA, Small Interfering / genetics
  • RNA, Small Interfering / metabolism
  • Receptors, Lysosphingolipid / genetics
  • Receptors, Lysosphingolipid / metabolism*
  • Receptors, Opioid, mu / antagonists & inhibitors
  • Receptors, Opioid, mu / genetics
  • Receptors, Opioid, mu / metabolism*
  • Thrombin / metabolism
  • Transcriptional Activation*
  • rho-Associated Kinases
  • rhoA GTP-Binding Protein / genetics
  • rhoA GTP-Binding Protein / metabolism


  • Analgesics, Opioid
  • Intracellular Signaling Peptides and Proteins
  • Narcotic Antagonists
  • Quaternary Ammonium Compounds
  • RNA, Small Interfering
  • Receptors, Lysosphingolipid
  • Receptors, Opioid, mu
  • methylnaltrexone
  • Enkephalin, Ala(2)-MePhe(4)-Gly(5)-
  • Naloxone
  • Naltrexone
  • Morphine
  • Protein Serine-Threonine Kinases
  • rho-Associated Kinases
  • Thrombin
  • rhoA GTP-Binding Protein