Cerebrospinal fluid biomarkers in experimental spinal nerve root injury

Study Design. Cerebrospinal fluid biomarkers were evaluated in a setup using established pig models to mimic clinical disc herniation. Objectives. To investigate biomarkers for nerve tissue injury, inflammation, and pain in cerebrospinal fluid after mechanical compression and/or nucleus pulposus application to spinal nerve roots. Summary of Background Data. The association between mechanical compression, biochemical effects of nucleus pulposus, and nerve root injury in degenerative disc disorders is incompletely investigated. Methods. The unilateral S1 nerve root was exposed in 20 pigs. The animals were divided into four groups (n=5 each): 1) slow-onset mechanical compression with an ameroid constrictor; 2) autologous nucleus pulposus application; 3) mechanical compression plus nucleus pulposus; and 4) sham operation. After 1 week, 6 mL of cerebrospinal fluid was collected, and four structural nerve proteins, neurofilaments, S-100, glial fibrillary acidic protein, neuron-specific enolase, the proinflammatory cytokine interleukin-8, the neurotransmitter nociceptin, and substance P endopeptidase activity were analyzed using immunoassays. Results. The concentration of neurofilament was increased in the mechanical compression group (17.0 mug/L+/-5.0) and in the mechanical compression plus nucleus pulposus group (19.8+/-12.1 mug/L) compared with the sham group (0.9+/-0.9 mug/L) and the nucleus pulposus group (0.4+/-0.1 mug/L) (P<0.01 for both). The concentration of nociceptin was increased significantly in the mechanical compression group (24.0 +/- 8.6 fm/mL) and in the mechanical compression plus nucleus pulposus group (31.2 +/- 6.6 fm/mL) compared with the sham group (7.0 +/- 1.3 fm/mL) (P<0.05 and P<0.01, respectively). A correlation was found between concentrations of neurofilament and nociceptin(r=0.50, P<0.05). There were no intergroup differences regarding glial fibrillary acidic protein, neuron-specific enolase, S-100, interleukin-8, or substance P endopeptidase activity. Conclusions. The present study demonstrates increased concentrations of neurofilament and nociceptin in cerebrospinal fluid after nerve root compression. A simultaneous application of nucleus pulposus did not increase the response.