Cytokine mRNA expression in painful radiculopathy

Abstract

Inflammatory cytokines contribute to lumbar radiculopathy. Regulation of cytokines for transient cervical injuries, with or without longer-lasting inflammation, remains to be defined. The C7 root in the rat underwent compression (10gf), chromic gut suture exposure (chr), or their combination (10gf+chr). Ipsilateral C7 spinal cord and dorsal root ganglia (DRG) were harvested at 1 hour after injury for real-time PCR analysis of IL-1beta, IL-6, and TNF-alpha. Cytokine mRNA increased after all 3 injuries. TNF-alpha mRNA in the DRG was significantly increased over sham after 10gf+chr (P = .026). Spinal IL-1beta was significantly increased over sham after 10gf and 10gf+chr (P < .024); IL-6 was significantly increased after 10gf+chr (P < .024). In separate studies, the soluble TNF-alpha receptor was administered at injury and again at 6 hours in all injury paradigms. Allodynia was assessed and tissue samples were harvested for cytokine PCR. Allodynia significantly decreased with receptor administration for 10gf and 10gf+chr (P < .005). Treatment also significantly decreased IL-1beta and TNF-alpha mRNA in the DRG for 10gf+chr (P < .028) at day 1. Results indicate an acute, robust cytokine response in cervical nerve root injury with varying patterns, dependent on injury type, and that early increases in TNF-alpha mRNA in the DRG may drive pain-related signaling for transient cervical injuries.

Perspective: Inflammatory cytokine mRNA in the DRG and spinal cord are defined after painful cervical nerve root injury. Studies describe a role for TNF-alpha in mediating behavioral sensitivity and inflammatory cytokines in transient painful radiculopathy. Results outline an early response of inflammatory cytokine upregulation in cervical pain.

Fig 1

Quantification of IL-1β (A), IL-6 (B), TNFα (C) mRNA expression in the ipsilateral DRG at 1 hour following sham, 10gf, chr, or 10gf+chr. Asterisk (*) indicates a significant difference from sham and the pound sign (#) indicates a significant difference from normal. At 1 hour after 10gf, chr, or 10gf+chr, IL-1β and TNFα mRNA were both significantly increased compared to normal (#, p<0.042). This increase was also significant compared to sham for TNFα following 10gf+chr (*,# p<0.026). Error bars indicate +/- standard deviation (SD).

Fig 2

Quantification of spinal cord IL-1β (A), IL-6 (B), TNFα (C) mRNA expression at 1 hour after sham, 10gf, chr, or 10gf+chr. At 1 hour following 10gf, chr, or 10gf+chr, IL-1β mRNA was significantly increased compared to normal (# p<0.005); this increase was also significant over sham for 10gf and 10gf+chr (*,# p<0.001). TNFα was also significantly increased compared to normal for 10gf and 10gf+chr (p<0.019). IL-6 mRNA were significantly increased after 10gf compared to normal and sham (*,# p<0.024). Error bars indicate +/- standard deviation (SD).

Fig 3

Average mechanical allodynia in the ipsilateral and contralateral forepaws at day 1 for sham, 10gf, 10gf+sTNFR1, chr, chr+sTNFR1, 10gf+chr, or 10gf+chr+sTNFR1. Allodynia is measured by the number of paw withdrawals for stimulation with each von Frey filament: (A) 1.4g, (B) 2g, and (C) 4g. Asterisk (*) indicates significant difference from sham values. Treatment with sTNFR1 significantly decreased allodynia compared to non-treatment responses for 10gf and 10gf+chr for testing with the 1.4g (A) filament. This trend was conserved across filaments for 10gf+chr injury (A,B,C). Error bars indicate +/- standard deviation (SD).

Fig 4

Quantification of cytokine gene expression in the ipsilateral DRG at 1 day after injury either with or without sTNFR1 treatment: IL-1β (A), IL-6 (B), TNFα (C). Treatment with sTNFR1 significantly decreased IL-1β and TNFα mRNA compared to their matched un-treated groups (p<0.028). Error bars indicate +/- standard deviation (SD).

Fig 5

Quantification of relative levels of IL-1β (A), IL-6 (B), TNFα (C) mRNA expression in the ipsilateral spinal cord at 1 day following 10gf or 10gf+chr, either with or without sTNFR1 treatment. Treatment with sTNFR1 decreased TNFα mRNA compared to un-treated rats. Error bars indicate +/- standard deviation (SD).