Abstract
Aims: Spinal fractures cause compression of the spinal cord, and nerve cells and nerve fibers are severely damaged. The immediate mechanical injury is subsequently enhanced in a process called secondary damage, and it has been proposed that inflammatory cells such as microglial cells and cytokines such as interleukin (IL)-1 damage nerves and nerve fibers that were initially not affected by spinal cord compression. It was the aim of this study a) to investigate the role of microglial cells and IL-1 in neuronal damage, and b) to investigate whether the anti-inflammatory agent IL-1 receptor antagonist (IL-1ra) that has been successfully used in patients with polyarthritis can protect neurons by inhibiting microglial activation or by antagonising cellular effects of IL-1.
Methods: We investigated the effects of IL-1 and IL-1ra on neurons and microglial cells in organotypic hippocampal slice cultures (OHSC): OHSC derived from rats were excitotoxically lesioned after 6 days in vitro by application of N-methyl-d-aspartate (NMDA) and treated with (IL)-1 (6 ng/ml) or IL-1ra (40, 100, or 500 ng/ml) for up to 10 days. OHSC were then quantitatively analyzed by confocal laser scanning microscopy after fluorescent labeling of neurons and microglial cells.
Results: Treatment of unlesioned OHSC with IL-1 did not induce neuronal damage although the number of microglial cells increased. NMDA-lesioning alone resulted in a massive increase in the number of microglial cells and degenerating neurons. Treatment of NMDA-lesioned OHSC with IL-1 exacerbated neuronal cell death and further enhanced microglial cell numbers. Treatment of NMDA-lesioned cultures with IL-1ra significantly attenuated NMDA-induced neuronal damage and reduced the number of microglial cells, whereas application of IL-1ra in unlesioned OHSC did not induce significant changes in either cell population.
Conclusion: Our findings indicate that a) IL-1 directly affects neurons and acts independently from infiltrating hematogenous cells, b) IL-1 induces microglial activation although it is not neurotoxic per se, c) IL-1 enhances excitotoxic neuronal damage and microglial activation, d) IL-1ra, even when only applied for short periods of time, reduces neuronal cell death and induces a dose-dependent decrease in the number of microglial cells after excitotoxic damage. These findings suggest that IL-1ra has the potential to exert beneficial effects in patients with spinal fractures, and this encourages further in vivo-studies.
Theses abstracts were prepared by Professor Roger Lemaire. Correspondence should be addressed to EFORT Central Office, Freihofstrasse 22, CH-8700 Küsnacht, Switzerland.
