The role of spinal thrombin through protease-activated receptor 1 in hyperalgesia after neural injury

J Neurosurg Spine. 2017 Apr;26(4):532-541. doi: 10.3171/2016.9.SPINE16501. Epub 2017 Jan 6.

Abstract

OBJECTIVE Painful neuropathic injuries induce blood-spinal cord barrier (BSCB) breakdown, allowing pro-inflammatory serum molecules to cross the BSCB, which contributes to nociception. The goal of these studies was to determine whether the blood-borne serine protease thrombin also crosses a permeable BSCB, contributing to nociception through its activation of protease-activated receptor-1 (PAR1). METHODS A 15-minute C-7 nerve root compression, which induces BSCB breakdown and painful behaviors by Day 1, was administered in the rat (n = 10); sham operation (n = 11) and a 3-minute compression (n = 10) that does not induce sensitivity were administered as controls. At Day 1 after root compression, spinal cord tissue was co-immunolabeled for fibrin/fibrinogen, the enzymatic product of thrombin, and IgG, a serum protein, to determine whether thrombin acts in areas of BSCB breakdown. To determine whether spinal thrombin and PAR1 contribute to hyperalgesia after compression, the thrombin inhibitor hirudin and the PAR1 antagonist SCH79797, were separately administered intrathecally before compression injuries (n = 5-7 per group). Rat thrombin was also administered intrathecally with and without SCH79797 (n = 6 per group) to determine whether spinal thrombin induces hypersensitivity in naïve rats through PAR1. RESULTS Spinal fibrin(ogen) was elevated at Day 1 after root compression in regions localized to BSCB breakdown and decreased in those regions by Day 7. Blocking either spinal thrombin or PAR1 completely prevented compression-induced hyperalgesia for 7 days. Intrathecal thrombin induced transient pain that was prevented by blocking spinal PAR1 before its injection. CONCLUSIONS The findings of this study suggest a potent role for spinal thrombin and its activation of PAR1 in pain onset following neuropathic injury.

Keywords: BSCB = blood–spinal cord barrier; CNS = central nervous system; DMSO = dimethyl sulfoxide; IgG = immunoglobulin G; PAR1 = protease-activated receptor-1; PBS = phosphate-buffered saline; blood–spinal cord barrier; pain; protease-activated receptor-1; radicular injury; thrombin.

MeSH terms

  • Animals
  • Antithrombins / pharmacology
  • Capillary Permeability / drug effects
  • Capillary Permeability / physiology
  • Central Nervous System Agents / pharmacology
  • Cervical Vertebrae
  • Disease Models, Animal
  • Fibrin / administration & dosage
  • Fibrin / antagonists & inhibitors
  • Fibrin / metabolism*
  • Hirudins / pharmacology
  • Hyperalgesia / drug therapy
  • Hyperalgesia / metabolism*
  • Injections, Spinal
  • Male
  • Pain / drug therapy
  • Pain / metabolism*
  • Pain / pathology
  • Pain Measurement
  • Peripheral Nervous System Diseases / drug therapy
  • Peripheral Nervous System Diseases / metabolism*
  • Peripheral Nervous System Diseases / pathology
  • Pyrroles / pharmacology
  • Quinazolines / pharmacology
  • Radiculopathy / drug therapy
  • Radiculopathy / metabolism*
  • Radiculopathy / pathology
  • Rats, Sprague-Dawley
  • Receptor, PAR-1 / antagonists & inhibitors
  • Receptor, PAR-1 / metabolism*
  • Spinal Cord / blood supply
  • Spinal Cord / drug effects
  • Spinal Cord / metabolism*
  • Spinal Cord / pathology

Substances

  • Antithrombins
  • Central Nervous System Agents
  • Hirudins
  • N3-cyclopropyl-7-((4-(1-methylethyl)phenyl)methyl)-7H-pyrrolo(3, 2-f)quinazoline-1,3-diamine
  • Pyrroles
  • Quinazolines
  • Receptor, PAR-1
  • Fibrin

Supplementary concepts

  • Neuropathy, Painful