Tumor necrosis factor-α levels correlate with postoperative pain severity in lumbar disc hernia patients: opposite clinical effects between tumor necrosis factor receptor 1 and 2

Elevated IL-1β and IL-6 levels in lumbar herniated discs in patients with sciatic pain

PURPOSE

Previous experimental models have shown that proinflammatory cytokines modulate peripheral and central nociception. However, the direct correlation between inflammation and pain in patients remains unclear. Our aim is to correlate the levels of inflammation in the spine with pre- and postoperative pain scores after discectomy.

METHODS

Paravertebral muscle, annulus fibrosus (AF) and nucleus pulposus (NP) biopsies were intraoperatively collected from ten lumbar disc hernia (LDH) patients suffering from chronic sciatic pain and, as painless controls, five scoliosis patients. IL-1β and IL-6 expressions in these biopsies were assessed by qPCR and western blot. The amount of pain, indicated on a 0-10 point visual analogue scale (VAS), was assessed 1 day before surgery and 6 weeks and 1 year after surgery. For analysis purposes, LDH patients were grouped into painful (VAS ≥ 3.5) and non-painful (VAS < 3.5). LDH painful patient group showed a onefold increased mRNA expression of IL-1β in the NP, and IL-6 in the AF and NP (p < 0.05 vs. controls).

RESULTS

By western blot analysis, both cytokines were clearly visible in all LDH biopsies, but not in controls. However, cytokine expression of the painful patient group did not differ from those of the non-painful patient group. In addition, there was no correlation between VAS scores and either marker.

CONCLUSIONS

These findings support the idea that LDH is accompanied by a local inflammatory process. Yet, the lack of correlation between IL-1β or IL-6 expression and the severity pain suggests that these cytokines may not play a leading role in maintaining a pain generating network.

miR23b ameliorates neuropathic pain in spinal cord by silencing NADPH oxidase 4

AIMS

Neuropathic pain is a well-known type of chronic pain caused by damage to the nervous system. Until recently, researchers have been primarily focused on identifying the cellular or chemical sources of neuropathic pain or have approached neuropathic pain via the basis of biological study. We investigated whether mmu-mir-23b (miR23b) infusion can alleviate pain by compensating for the abnormally downregulated miR23b by reducing the expression of its target gene, NADPH oxidase 4 (NOX4), a reactive oxygen species (ROS) family member overexpressed in neuropathic pain.

RESULTS

Ectopic miR23b expression effectively downregulated NOX4 and was normalized to GAD65/67 expression. Moreover, the animals with neuropathic pain showed significant improvements in the paw withdrawal thresholds following miR23b infusion. Normalizing miR23b expression in tissue lesions caused by neuropathic pain induction reduced inflammatory mediator expression and increased the level of several ROS scavengers. Moreover, GABAergic neurons coexpressed suboptimal levels of miR23b and elevated NOX4/ROS after pain induction at the cellular level. MiR23b protects GABAergic neurons against ROS/p38/JNK-mediated apoptotic death. By evaluating the functional behavior of the mice receiving pain/miR23b, normal/anti-miR23b, or anti-miR23b/si-NOX4, the positive role of miR23b and the negative role of NOX4 in neuropathic pain were confirmed.

INNOVATION AND CONCLUSION

Based on this study, we conclude that miR23b plays a crucial role in the amelioration of neuropathic pain in the injured spinal cord by inactivating its target gene, NOX4, and protecting GABAergic neurons from cell death. We finally suggest that miR23b may provide attractive diagnostic and therapeutic resources for effective pain modulation in neuropathic pain.

The thalidomide analgesic effect is associated with differential TNF-α receptor expression in the dorsal horn of the spinal cord as studied in a rat model of neuropathic pain

The proinflammatory cytokine tumor necrosis factor-α (TNF-α) is well recognized as a key player in nociceptive signaling. Yet, therapeutic capitalization of this knowledge requires a better understanding of how TNF receptors (TNFR) contribute to pain. To address this question, we studied TNFR expression in the chronic sciatic nerve constriction (CCI) model of neuropathic pain. CCI and sham operated rats received two subcutaneous injections (one immediately after surgery, the other on postoperative day 5) containing either saline, GABA-reuptake inhibitor (NO-711), insulin-like growth factor-1 (IGF-1), ZVAD or thalidomide. Mechanical (using von Frey filaments) and thermal hypersensitivity (Hargreaves test) were assessed preoperatively and weekly during the first four postoperative weeks. Spinal cord dorsal horn samples were collected from animals that were sacrificed at 2 weeks and 4 weeks after surgery, and analyzed for TNFR1 and TNFR2 mRNA levels by qPCR and protein levels by Western blot. Compared to saline, all applied drug treatments resulted in a faster recovery from mechanical and thermal hypersensitivity, yet in a potency order of thalidomide>ZVAD=IGF-1>NO-711. CCI resulted in increased TNFR1 and TNFR2 mRNA and protein levels in the ipsilateral dorsal horn. Thalidomide was the only treatment that attenuated these increases. Finally, animals that showed a poor behavioral recovery were characterized by a significantly higher TNFR1/TNFR2 mRNA ratio. These data show that differential expression of TNFR in the dorsal horn is associated with recovery from pain in this model and suggest that the analgesic effects of thalidomide may act via this mechanism.