The aim of this work was to investigate putative biomarkers of neuronal plasticity and repair in the central nervous system. The effects of different disease processes, such as inflammation, demyelination and neurodegeneration were explored. We developed and validated ELISA-based assays for the quantification of neural cell adhesion molecule (NCAM) and growth-associated protein (GAP)-43, two known facilitators of neuronal outgrowth in the nervous system. NCAM isoforms in biological samples were characterised using mass spectrometry. Soluble NCAM was measured in in-vitro and in-vivo models of inflammation/demyelination and neurodegeneration, and across different neurological disorders in the CSF to understand the impact of inflammation and axonal loss on its levels. Recombinant GAP-43 was produced using baculovirus technology and purified in appreciable amounts for use in a new ELISA. Soluble GAP-43 levels were quantified across different neurological disorders in the CSF. Values for CSF NCAM and GAP-43 were correlated with clinical outcome measures. CSF NCAM demonstrated a restricted pattern of expression compared to that of serum whilst GAP-43 is almost exclusively expressed in the CSF, indicating that these biomarkers are intrathecally synthesised. CSF NCAM and GAP-43 levels were lower in neurological disorders with prominent axonal injury; multiple sclerosis, movement disorders, motor neurone disease, Alzheimer’s disease and meningitis. In vitro neuronal cell culture model and in vivo experimental autoimmune encephalomyelitis studies demonstrate that CSF NCAM correlates well with disease progression in multiple sclerosis. A similar relationship was not found with CSF GAP-43. In conclusion, the adult CNS may possess the intrinsic capacity to repair, but this capacity may be dramatically reduced in disease states. Measuring this process may be important in understanding neuronal repair and plasticity
