Systemic administrations of protamine heal subacute spinal cord injury in mice

Spinal cord injury (SCI) results in damage to neural circuits that cause long-term locomotor and sensory disability. The objective of the present study is to evaluate whether a clinical drug, protamine, can be employed as a therapeutic agent for SCI. First, we examined the rescue effect of protamine on dystrophic endballs (DEs) cultured on a chondroitin sulfate (CS) gradient coating. Consequently, axons with DE, which are unable to grow through the CS barrier, resumed growth after protamine treatment and were able to pass through the barrier. In addition, we tested whether protamine resolves the DE phenotype, accumulation of autophagosomes. The results demonstrated that protamine has significantly reduced the density of LC3 in DEs. Subsequently, mice were administered 1 mg/kg protamine via the tail vein one week following a contusion injury to the thoracic spinal cord. The hindlimb movements of the mice were evaluated in order to assess the therapeutic effect of protamine. Eleven venous administrations of protamine improved the symptoms. The current study has demonstrated that protamine cancels the CS inhibitory effect on axonal regrowth. Administrations of protamine were observed to alleviate hindlimb motor dysfunction in SCI mice. Our results suggest an effective therapeutic agent for SCI and a possibility for drug repositioning. It would be of interest to see if protamine also exerts a therapeutic effect in brain injury.