Cytokine expression in the epidural space: a model of noncompressive disc herniation-induced inflammation.
METHODS
Animal study.


OBJECTIVE
Development of an animal model for the study of biochemical changes that occur in the epidural space after intervertebral disc herniation.


BACKGROUND
Although strong evidence for an inflammatory component exists, the biochemical processes underlying pain after disc herniation remain unknown.


METHODS
Epidural lavage was performed in 48 rats after L5 dorsal root ganglion exposure at baseline and 3, 6, or 24 hours after placement of autologous nucleus pulposus (NP) (N = 15), saline (N = 15), or NP + an interferon-γ antibody (anti-IFN-γ; N = 18) directly onto the dorsal root ganglion. Multiplex assays quantifying interleukin (IL)-1α, IL-1β, IL-2, IL-4, IL-6, IL-10, tumor necrosis factor α (TNF-α), IFN-γ, and granulocyte-macrophage colony-stimulating factor (GM-CSF) were performed. NP (N = 7) was also analyzed for these cytokines by placing NP into saline and measuring the relative concentration.


RESULTS
Cytokines measured low at baseline (0-100 pg/mL) in all groups. Compared with saline, NP application caused IL-6 elevation, peaking at T = 3 hours, that was prevented by anti-IFN-γ. NP induced elevation of TNF-α, peaking at T = 24 hours and was prevented by anti-IFN-γ. IFN-γ was elevated after NP at T = 3 hours and T = 24 hours. IL-1α was similar after saline versus NP. The concentrations of IL-1β and IL-10 were elevated at T = 3 hours, 6 hours, and 24 hours in all groups without between-groups difference. The level of IL-4 peaked at T = 3 hours in the NP group and was different than saline and NP + anti-IFN-γ groups, but the time effect was insignificant. There was no change for GM-CSF. The concentration of cytokines measured in normal NP was less than 2 pg/mL for all cytokines except TNF-α.


CONCLUSIONS
In this model of acute noncompressive disc herniation, NP caused the elevation of epidural IL-6, TNF-α, and IFN-γ--all attenuated by IFN-γ blockade. IL-1β and IL-10 were both significantly elevated by saline alone and their response was not prevented by IFN-γ blockade. This model may prove useful for the study of the biochemical processes by which NP induces inflammation-induced nerve root irritation and radiculopathic pain.
Department of Orthopaedic Surgery, NYU Hospital for Joint Diseases, New York, NY 10003, USA. Jason.cuellar@nyumc.org
Jason M
JM
Cuéllar
Paula M
PM
Borges
Vanessa Gabrovsky
VG
Cuéllar
Andrew
A
Yoo
Gaetano J
GJ
Scuderi
David C
DC
Yeomans
D000818:Animals; D003050:Coccyx; D016207:Cytokines / Q000096:biosynthesis* / Q000235:genetics; D004195:Disease Models, Animal; D004824:Epidural Space / Q000378:metabolism; D005786:Gene Expression Regulation; D007405:Intervertebral Disc Displacement / Q000378:metabolism* / Q000473:pathology; D008297:Male; D011843:Radiculopathy / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D011897:Random Allocation; D051381:Rats; D017207:Rats, Sprague-Dawley
D016207:Cytokines