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.