Inhibiting IκB kinase-β downregulates inflammatory cytokines in injured discs and neuropeptides in dorsal root ganglia innervating injured discs in rats.
METHODS
Quantitative and immunohistological analysis of the efficacy of an IκB kinase-β (IKKβ) inhibitor in an injured intervertebral disc (IVD) model.


OBJECTIVE
To elucidate the efficacy of an IKKβ inhibitor on inflammatory cytokine levels in injured IVDs or on neuropeptide levels in the dorsal root ganglia (DRG) neurons innervating injured IVDs in rats.


BACKGROUND
Multiple studies have suggested that upregulation of inflammatory cytokines in damaged IVDs causes discogenic low back pain. The efficacy of blocking individual inflammatory cytokines is limited; however, inflammatory cytokine stimuli often require IKKβ to activate nuclear factor-k B.


METHODS
Sprague-Dawley rats were divided into 3 groups: sham, saline (disc-injury plus saline), and IKKβ (disc-injury plus anti-IKKβ). To induce injury, IVDs were repeatedly punctured.Experiment 1: Four, 7, and 14 days postinjury, coccygeal (Co) 5/6, Co6/7, and Co7/8 IVDs were resected and tumor necrosis factor-α, interleukin (IL)-1β, and IL-6 levels were quantified by enzyme-linked immunosorbent assay. Experiment 2: The neurotracer Fluoro-Gold was injected into injured L5-L6 IVDs and uninjured sham group IVDs to detect DRG neurons. One week postsurgery, L1-L6 DRGs were immunolabeled with the neuropeptide calcitonin gene-related peptide. The proportions of Fluoro-Gold-labeled calcitonin gene-related peptide-immunoreactive DRG neurons were assessed.


RESULTS
Experiment 1: IVD levels of tumor necrosis factor-α (through 2 wk), IL-1β (at 4 d), and IL-6 (at 4 d) were significantly higher in the saline group than in the sham group, and significantly lower in the IKKβ group than in the saline group (P < 0.05). Experiment 2: The percentage of calcitonin gene-related peptide-immunoreactive Fluoro-Gold-labeled DRG neurons was significantly higher in the saline group than in the sham group, and significantly lower in the IKKβ group than in the saline group (P < 0.05).


CONCLUSIONS
Injury-induced upregulation of inflammatory cytokines within IVDs and increased levels of neuropeptides within DRG neurons can be suppressed by inhibiting IKKβ.


METHODS
N/A.
*School of Medicine, Chiba University, Chiba, Japan †Department of Orthopaedic Surgery, Graduate School of Medicine, Chiba University, Chiba, Japan ‡IMMD Inc., Tokyo, Japan §Chiralgen Ltd., Chiba, Japan ¶Department of Orthopaedic Surgery, Toho University Sakura Medical Center, Sakura, Japan ‖Department of Orthopaedic Surgery, Teikyo University Chiba Medical Center, Chiba, Japan.
Sayako
S
Kobori
Masayuki
M
Miyagi
Sumihisa
S
Orita
Takefumi
T
Gemba
Tetsuhiro
T
Ishikawa
Hiroto
H
Kamoda
Miyako
M
Suzuki
Takatoshi
T
Hishiya
Toshihide
T
Yamada
Yawara
Y
Eguchi
Gen
G
Arai
Yoshihiro
Y
Sakuma
Yasuhiro
Y
Oikawa
Yasuchika
Y
Aoki
Tomoaki
T
Toyone
Kazuhisa
K
Takahashi
Gen
G
Inoue
Seiji
S
Ohtori
D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism*; D015536:Down-Regulation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005727:Ganglia, Spinal / Q000378:metabolism* / Q000503:physiopathology; D051550:I-kappa B Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D007150:Immunohistochemistry; D018836:Inflammation Mediators / Q000378:metabolism; D053583:Interleukin-1beta / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D007403:Intervertebral Disc / Q000293:injuries / Q000294:innervation / Q000378:metabolism*; D008159:Lumbar Vertebrae / Q000293:injuries / Q000294:innervation / Q000378:metabolism; D008297:Male; D009474:Neurons / Q000378:metabolism; D009479:Neuropeptides / Q000378:metabolism*; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism
D016207:Cytokines; D004791:Enzyme Inhibitors; D018836:Inflammation Mediators; D053583:Interleukin-1beta; D015850:Interleukin-6; D009479:Neuropeptides; D014409:Tumor Necrosis Factor-alpha; D051550:I-kappa B Kinase; D015740:Calcitonin Gene-Related Peptide