Pretreatment with Calpain Inhibitor CEP‐4143 Inhibits Calpain I Activation and Cytoskeletal Degradation, Improves Neurological Function, and Enhances Axonal Survival After Traumatic Spinal Cord Injury

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Abstract
The pathophysiology of traumatic spinal cord injury (SCI) involves abnormal activation of the neutral cysteine protease calpain I (EC 3.4.22.17). In the present study we examined the effect of the calpain inhibitor CEP‐4143 on cytoskeletal protection and neurological recovery after SCI in adult rats. Microinjection of 50 mM CEP‐4143 into the T7 vertebral segment 10 min before a 35‐g clip compression injury resulted in inhibition of calpain activation at 2 and 4 h postinjury, as determined by western blotting for calpain I‐mediated spectrin degradation, and significantly attenuated the degradation of dephosphorylated NF200 neurofilament protein at 4 and 8 h postinjury. To examine the in vivo chronic neuroprotective effects of CEP‐4143, animals underwent microinjection with saline or 50 mM CEP‐4143 10 min before injury, followed by weekly blinded behavioral assessments for 6 weeks. Animals receiving CEP‐4143 treatment showed significant improvement over saline‐treated controls on the Basso Beattie Bresnahan locomotor rating scale (p < 0.02) and inclined plane test (p < 0.05). Counts of neurons in the red nucleus retrogradely labeled by fluorogold after introduction distal to the injury site were significantly higher in CEP‐4143‐treated animals. Finally, morphometric assessment of the injury site by computer‐assisted image analysis revealed significant tissue preservation in CEP‐4143‐treated animals. We conclude that the calpain antagonist CEP‐4143 exhibits biochemical, behavioral, and anatomical neuroprotection following traumatic SCI.