The role of enhanced cutaneous IL-1beta signaling in a rat tibia fracture model of complex regional pain syndrome

Pain. 2009 Aug;144(3):303-313. doi: 10.1016/j.pain.2009.04.033. Epub 2009 May 26.

Abstract

Tibia fracture in rats initiates a syndrome resembling the complex regional pain syndrome type I. Accumulating evidence indicates that IL-1beta is involved in the modulation of nociceptive information and it acts as an intermediate inflammatory mediator via up-regulation of NGF. We hypothesized that IL-1beta signaling might mediate the development of the CRPS-like changes after tibial fracture, either directly or by stimulating NGF expression. Rats underwent distal tibia fracture and casting for 4 weeks and were chronically treated with an IL-1 receptor antagonist (IL-1ra). Nociceptive testing and assessment of edema and hindpaw warmth were performed at baseline and after cast removal. Bone microarchitecture was evaluated by micro-computed tomography. Confocal immunofluorescence and in situ hybridization techniques were used to evaluate changes in the cutaneous expression of IL-1beta at 4 weeks post-fracture. The nociceptive and vascular effects of intraplantar IL-1beta injections were evaluated in intact rats at different time points after injection. We found that: (1) IL-1ra reduced fracture-induced nociceptive sensitization, but did not decrease hindpaw edema or warmth, (2) fracture chronically up-regulated IL-1beta mRNA and protein expression in hindpaw skin keratinocytes, (3) IL-1beta intraplantar injection induced mechanical allodynia in a dose-dependent manner and stimulated keratinocyte NGF expression in the hindpaw skin, and (4) intraplantar injection of NGF-induced nociceptive sensitization. Collectively, these results indicate that cutaneous IL-1beta signaling can contribute to chronic regional nociceptive sensitization after fracture, possibly by stimulating NGF over-expression in keratinocytes. Our data also highlight the importance of the keratinocyte as the primary source of post-traumatic IL-1beta over-expression.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • Disease Models, Animal
  • Edema / etiology
  • Edema / physiopathology
  • Foot / innervation
  • Foot / physiopathology
  • Gene Expression Regulation / drug effects
  • Gene Expression Regulation / physiology
  • Hyperemia / etiology
  • Hyperemia / physiopathology
  • Inflammation / etiology
  • Inflammation / metabolism*
  • Inflammation / physiopathology
  • Interleukin 1 Receptor Antagonist Protein / pharmacology
  • Interleukin-1beta / antagonists & inhibitors
  • Interleukin-1beta / genetics
  • Interleukin-1beta / metabolism*
  • Keratinocytes / metabolism*
  • Male
  • Nerve Growth Factor / metabolism*
  • Nerve Growth Factor / pharmacology
  • Nociceptors / metabolism*
  • Pain Measurement
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Reflex Sympathetic Dystrophy
  • Sensory Receptor Cells / metabolism*
  • Skin / innervation*
  • Skin / physiopathology
  • Tibial Fractures / complications
  • Up-Regulation / physiology

Substances

  • Interleukin 1 Receptor Antagonist Protein
  • Interleukin-1beta
  • RNA, Messenger
  • Nerve Growth Factor