Purpose and Background: We have previously reported our investigations of nerve ingrowth into intervertebral discs (IVD) from patients with mechanical low back pain. We have shown that in discs that are painful on discography (pain level discs) nerves actively grow into the deep annulus fibrosus and nucleus pulposus. Nerve ingrowth accompanies blood vessel ingrowth and advances into the nucleus pulposus from the end plate. The morphology and neurochemistry of these nerves indicate them to be nociceptive.

The growth of non-myelinated pain fibres in other settings is regulated by the cytokine Nerve Growth Factor (NGF). In this study, we have investigated the production and distribution of NGF, or more particularly its active isoform – NGF-β, and its receptors, in diseased intervertebral discs in order to establish whether this cytokine might be responsible for the observed nerve ingrowth in this situation.

Methods: Tissue sections of 21 pain level, 15 non-pain level diseased and 12 normal intervertebral discs, taken at the time of spinal surgery, and from cadavers, were probed by radioactive in situ hybridisation (ISH) for expression of NGF-β, and by immunohistochemistry (IHC) for its high and low affinity receptors (trk-A and p75 respectively). In addition, either serial sections were stained with cell specific markers (CD31 – endothelial cell, PGP9.5 – neurones, GAP43 – actively growing nerves) or sections were doubled stained (two antibodies or both ISH and IHC).

Results: We have demonstrated that NGF-β is synthesised by the endothelial cells of blood vessels growing into the IVD from the end plate. The high affinity receptor is expressed by those small nerve fibres that accompany the vessels and in their offshoots in pain level discs that are growing from perivascular nerves into the disc. In addition to their expressing the nerve specific molecule PGP9.5, the trk-A positive cells also express the nerve growth associated protein GAP43.

Conclusion: The data indicate that nerve ingrowth into IVD is regulated by NGF-β. We have localised this production to the endothelial cells of ingrowing blood vessels. NGF-β is a potential therapeutic target for the management of back pain.

Purpose and Background: There is increasing evidence that events within the diseased intervertebral disc (IVD) are mediated by locally synthesised cytokines. A prominent histological, imaging and surgical feature of IVD disease is degradation of the cartilaginous discal matrix. Whilst the mechanism by which this is mediated is unknown, in other situations where connective tissues are degraded degradation is the result of production of matrix-degrading enzymes by local connective tissue cells stimulated by cytokines, particularly the beta isoform of interleukin-1 (IL-1β). Included amongst these disorders is osteoarthritis (OA) of diarthrodial joints. OA has many similarities to the discal “degeneration” seen in mechanical back pain syndromes. In the current study, we have used a combination of in-situ techniques to establish if IL-1β is responsible for stimulating matrix degradation in the IVD.

Methods: Using a combination of radioactive in-situ hybridisation (ISH) and competitive in situ zymography (ISZ) we have studied expression of IL-1β and IL-1R – its type 1 receptor (ISH) and matrix degradation (ISZ) in five diseased lumbar IVD taken at spinal fusion surgery and 10 cadaveric IVD (five normal and five diseased). The nucleus pulposus (NP) was separated from the annulus fibrosus and diced into 0.5cm cubes. Half the cubes (typically three) were fixed in formalin and processed into paraffin wax for ISH, and half were used for ISZ. For ISH, 5 μm sections of paraffin-embedded tissue were reacted with cDNA probes radiolabelled with 35S to 580 and 530 base segments of the IL-1β and IL-1R molecules. Hybridisation was disclosed using autoradiography. For ISZ, 50 μm vibratome sections were placed into wells on microscope slides precoated with gelatin. Sections were incubated for 10 days, half in culture medium and half in medium supplemented with human recombinant IL-1 receptor antagonist (IL-1Ra – an inhibitor of IL-1). Sections were photographed at daily intervals to detect evidence of gel degradation.

Results: Chondrocytes within patient and cadaveric diseased but not normal discs expressed mRNA for both IL-1β and IL-1R. By ISZ, the same cells degraded gelatin. Degradation was inhibited by recombinant IL-1Ra.

Conclusion: This study shows that chondrocytes of diseased discs express IL-1 and its receptor. The same cells produced matrix-degrading enzymes by a mechanism that can be inhibited by the IL-1 inhibitor IL-1Ra. IL-1 is a potential therapeutic target for the management of IV disc disease.