A novel calpain inhibitor, ((1S)-1-((((1S)-1-Benzyl-3-cyclopropylamino-2,3-di-oxopropyl)amino)carbonyl)-3-methylbutyl)carbamic acid 5-methoxy-3-oxapentyl ester (SNJ-1945), reduces murine retinal cell death in vitro and in vivo.

We examined whether ((1S)-1-((((1S)-1-benzyl-3-cyclopropylamino-2,3-di-oxopropyl)amino)carbonyl)-3-methylbutyl)carbamic acid 5-methoxy-3-oxapentyl ester (SNJ-1945), a new orally available calpain inhibitor, might reduce retinal cell death in vivo and/or in vitro. Retinal cell damage was induced in vivo in mice by intravitreal injection of N-methyl-d-aspartate (NMDA), and SNJ-1945 was intraperitoneally or orally administered twice. NMDA-induced calpain activity (measured as the cleaved products of alpha-spectrin) and its substrate, p35 (a neuron-specific activator for cyclin-dependent kinase 5), in the retina were examined by immunoblotting. In RGC-5 (a rat retinal ganglion cell line) cell culture, cell damage was induced by a 4-h oxygen-glucose deprivation (OGD) treatment followed by an 18-h reoxygenation period. In mouse retinas, SNJ-1945 (30 or 100 mg/kg i.p., 100 or 200 mg/kg p.o.) significantly inhibited the cell loss in the ganglion cell layer (GCL) and the thinning of the inner plexiform layer induced by NMDA. Furthermore, the number of positive cells for terminal deoxynucleotidyl transferase dUTP nick-end labeling was significantly reduced in the GCL and the inner nuclear layer of retinas treated with SNJ-1945 compared with vehicle-treated retinas 24 h after NMDA injection. Levels of cleaved alpha-spectrin products increased and p35 decreased 6 h after NMDA injection or later, and their effects were attenuated by SNJ-1945. In vitro, SNJ-1945 (10 and 100 muM) inhibited the OGD stress-induced reduction in cell viability. In conclusion, SNJ-1945 may afford valuable neuroprotection against retinal diseases, because it was effective against retinal damage both in vitro and in vivo. Our results also indicate that calpain activation and subsequent p35 degradation may be involved in the mechanisms underlying retinal cell death.