Axonal damage induced by cerebrospinal fluid from patients with relapsing-remitting multiple sclerosis

The importance of axonal damage in multiple sclerosis (MS) has been recentl y stressed in proton magnetic resonance spectroscopy and pathological studi es, but the exact mechanism producing this damage is unknown. The aim of ou r study was to ascertain whether soluble mediators present in the cerebrosp inal fluid (CSF) of patients with relapsing-remitting MS could induce neuro n injury in culture. Different biochemical and cytochemical parameters were determined in primary embryonal rat neuron cultures following 8 days of ex posure to CSF. Cytotoxic activity was evaluated with a blue formazan produc tion colorimetric assay. Morphological and immunocytochemical studies perfo rmed with antibodies against beta-tubulin revealed neuritic fragmentation, axonal damage and cellular shrinkage indicating apoptosis, Detection of apo ptosis was carried out using the fluorescent DNA-binding dye Hoechst 33342, as well as by a Terminal deoxynucleotidyl transferase-mediated dUTP Nick E nd-Labeling assay. We observed that soluble factors in CSF from patients wi th "aggressive" MS i.e, those with poor recovery after relapses, induced ne urite breakdown and neuronal apoptosis in cultures. Neuron injury is not re lated with blood-brain barrier dysfunction nor with IgG index. Interestingl y, CSF from patients with "non-aggressive" MS i.e., relapsing-remitting pat ients with a good recovery after relapses, did not induce any damage. In co nclusion, we report that CSF from patients with aggressive MS bears soluble mediators that induce axonal damage and apoptosis of neurons in culture. T hese mediators can be present during the first attack of the disease, and t he neuronal damage caused could be related to the functional deficit of the se MS patients. (C) 2000 Published by Elsevier Science B.V. All rights rese rved.