Pharmacological analysis of the cortical neuronal cytoskeletal protective efficacy of the calpain inhibitor SNJ-1945 in a mouse traumatic brain injury model

The efficacy of the amphipathic ketoamide calpain inhibitor SNJ-1945 in attenuating calpain-mediated degradation of the neuronal cytoskeletal protein -spectrin was examined in the controlled cortical impact (CCI) traumatic brain injury (TBI) model in male CF-1 mice. Using a single early (15min after CCI-TBI) i.p. bolus administration of SNJ-1945 (6.25, 12.5, 25, or 50-mg/kg), we identified the most effective dose on -spectrin degradation in the cortical tissue of mice at its 24h peak after severe CCI-TBI. We then investigated the effects of a pharmacokinetically optimized regimen by examining multiple treatment paradigms that varied in dose and duration of treatment. Finally, using the most effective treatment regimen, the therapeutic window of -spectrin degradation attenuation was assessed by delaying treatment from 15min to 1 or 3h post-injury. The effect of SNJ-1945 on -spectrin degradation exhibited a U-shaped doseresponse curve when treatment was initiated 15min post-TBI. The most effective 12.5mg/kg dose of SNJ-1945 significantly reduced -spectrin degradation by similar to 60% in cortical tissue. Repeated dosing of SNJ-1945 beginning with a 12.5mg/kg dose did not achieve a more robust effect compared with a single bolus treatment, and the required treatment initiation was less than 1h. Although calpain has been firmly established to play a major role in post-traumatic secondary neurodegeneration, these data suggest that even brain and cell-permeable calpain inhibitors, when administered alone, do not show sufficient cytoskeletal protective efficacy or a practical therapeutic window in a mouse model of severe TBI. Such conclusions need to be verified in the human clinical situation.