Amiodarone Improves Locomotor Function in Experimental Spinal Cord Injury by Reducing Secondary Axonal Degeneration and White Matter Atrophy

Secondary loss of initially spared white and grey matter is a major driver of morbidity after spinal cord injury (SCI). Current treatments have not substantially changed in decades and are limited to surgical decompression and blood pressure management. White matter atrophy after SCI is primarily caused by secondary axonal degeneration (SAD), which is triggered by maladaptive axonal uptake of sodium and calcium through a multitude of ion channels and transporters. While specific inhibitors have been studied, none have been translated into clinical use, in part due to the diverse array of involved channels. Here, we studied whether amiodarone, an FDA-approved antiarrhythmic drug that exerts pleotropic inhibition of multiple sodium and calcium channels, might be neuro- and axonoprotective after SCI precisely because of its broad inhibitory profile. Mice were submitted to off-midline thoracic SCI versus sham surgery and treated with amiodarone versus vehicle control within 15 min and after 4 h of injury. We found that amiodarone treatment after SCI improved locomotor function, which was longitudinally measured over 28 days with the Basso mouse scale, accelerating rotarod, and inclined plane tests. Amiodarone treatment reduced spinal cord atrophy and white matter loss at 28 days after injury, assessed by spinal cord wet weights and by volumetric measurements of grey and white matter in serial coronal sections of spinal cords stained with luxol fast blue and cresyl violet. Amiodarone was directly axonoprotective after SCI, with reduced losses of neurofilament heavy positive axons at 28 days. Interestingly, long-term amiodarone-mediated axonoprotection was accompanied by a reduction of SAD at early time points, measured by counting axonal spheroids 24 h after SCI in fluorescently labeled corticospinal tract axons imaged with light sheet imaging. Overall, these data identify amiodarone as a potentially axonoprotective agent that could be repurposed to treat secondary injury after SCI.