Calpain inhibitor MDL 28170 protects hypoxic-ischemic brain injury in neonatal rats by inhibition of both apoptosis and necrosis.

MDL 28170 is a CNS-penetrating calpain inhibitor, and we examined the effects of MDL 28170 on hypoxic-ischemic brain injury in immature brain using the Rice-Vannucci model. Immediately after hypoxic exposure, 24 mg/kg of MDL 28170 was injected intraperitoneally as an initial dose, followed by 12 mg/kg every 4 h for a total dose of 60 mg/kg over 12 h post-HI. A vehicle control group received peanut oil injection instead. Macroscopic evaluation of brain injury revealed the neuroprotective effect of MDL 28170 after 12 h post-HI. Neuropathological quantitative analysis of cell death showed that MDL 28170 significantly decreased the number of necrotic cells in all the examined regions except for cingular cortex, and the number of apoptotic cells in caudate putamen, parietal cortex, hippocampus CA1, and laterodorsal thalamus. Western blots showed that MDL 28170 suppressed 145/150 kDa subunits of alpha-spectrin breakdown products (SBDP) in cortex, hippocampus, thalamus, and striatum, and also 120-kDa subunit of SBDP in all regions except for striatum. This suggests that MDL 28170 inhibited activation of calpain and caspase-3, respectively. Our results indicate that post-hypoxic MDL 28170 injection is neuroprotective in HI newborn rat brain by decreasing both necrosis and apoptosis. SBDP expression also suggests that MDL 28170 injection inhibits both calpain and caspase-3 activation after HI insult.