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

Abstract

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.

Fig. 1

Distribution of individual IL-1β (a–c) and IL-6 (d–f) mRNA levels in muscle (a, d), annulus fibrosus (b, e) and nucleus pulposus (c, f) samples from LDH patients and scoliosis controls (n = 5). Based on 1-year follow-up VAS scores, the LDH patient group was divided in a painful (VAS ≥ 3.5; n = 5) and a non-painful (VAS < 3.5; n = 5) outcome group. Expression levels were normalized to GAPDH as reference gene and are represented as time-fold increase over controls. NS Non-significant, *p < 0.05 and **p < 0.01

Fig. 2

Distribution of individual IL-1β (a–c) and IL-6 (d–f) protein levels in muscle (a, d), annulus fibrosus (b, e) and nucleus pulposus (c, f) samples from LDH patients, and representative western blot for protein expression. Based on 1-year follow-up VAS scores, the LDH patient group was divided in a painful (VAS ≥ 3.5; n = 5) and a non-painful (VAS < 3.5; n = 5) outcome group. Protein levels were normalized to β-actin. Particularly IL-6 was clearly present in annulus fibrosus and nucleus pulposus samples (e, f). There were no significant differences between both patient groups for either cytokine in either tissue type. M muscle, AF annulus fibrosus, NP nucleus pulposus

Fig. 3

Within the LDH patient group, VAS scores at 1 year follow-up did not correlate with IL-1β mRNA levels in annulus fibrosus (a, r = 0.03), IL-1β mRNA levels in nucleus pulposus (b, r = 0.05), IL-6 mRNA levels in annulus fibrosus (c, r = −0.11) or with IL-6 mRNA levels in nucleus pulposus (d, r = 0.23)

Fig. 4

Within the LDH patient group, VAS scores at 1 year follow-up did not correlate with IL-1β protein levels in annulus fibrosus (a, r = 0.02), IL-1β protein levels in nucleus pulposus (b, r = −0.08), IL-6 protein levels in annulus fibrosus (c, r = −0.24) or with IL-6 protein levels in nucleus pulposus (d, r = −0.31)