The novel calpain inhibitor SJA6017 improves functional outcome after delayed administration in a mouse model of diffuse brain injury

A principal mechanism of calcium-mediated neuronal injury is the activation of neutral proteases known as calpains. Proteolytic substrates for calpain include receptor and cytoskeletal proteins, signal transduction enzymes an d transcription factors. Recently, calpain inhibitors have been shown to pr ovide benefit in rat models of focal head injury and focal cerebral ischemi a. The present study sought to investigate, in experiment 1, the time cours e of calpain-mediated cytoskeletal injury in a mouse model of diffuse head injury by measuring the 150- and 145-kDa alpha -spectrin breakdown products (SBDP). Secondly, in experiment 2, we examined the effect of early (20 min postinjury) administration of the novel calpain inhibitor SJA6017 on funct ional outcome measured 24 h following injury and its effect on posttraumati c ce-spectrin degradation. Lastly, in experiment 3, we examined the effect of delayed (4 or 6 h postinjury) administration of SJA6017 on 24-h postinju ry functional outcome. In experiment 1, isoflurane-anesthetized male CF-1 m ice (18-22 g) were subjected to a 750 g-cm weight drop-induced injury and w ere sacrificed for SBDP analysis at postinjury times of 30 min, and 1, 2, 6 , 24 and 48 h (plus sham). In experiments 2 and 3, mice were injured as des cribed, and delivered a single tail vein injection of either SJA6017 (0.3, 1, or 3 mg/kg) or vehicle (administered immediately, 4 or 6 h postinjury [3 mg/kg]). Functional outcome was evaluated in both studies, and, in experim ent 2, 24-h postinjury assessment of SBDPs was determined. Following injury , the level of SBDP 145 was significantly different from sham at 24 and 48 h in cortical and at 24 h in the hippocampal tissues and at 48 h in the str iatum. Immediate postinjury administration of SJA6017 resulted in a dose-re lated improvement in 24-h functional outcome (p < 0.05 at 3 mg/kg). Signifi cance was maintained after a 4-h delay of the 3 mg/kg, but was lost after a 6-h delay. Despite improvement in functional outcome at 24 h, SJA6017 did not reduce spectrin breakdown in cortical or hippocampal tissues. These res ults support a role for calpain-mediated neuronal injury and the potential for a practical therapeutic window for calpain inhibition following traumat ic brain injury. However, measurements of regional spectrin degradation may not be the most sensitive marker for determining the effects of calpain in hibition.