Oral administration of crocetin prevents inner retinal damage induced by N-methyl-d-aspartate in mice

Crocetin, an aglycone of crocin, is found in stigmas of the saffron crocus (Crocus starus L.) and has been used in traditional medicine. We investigated the effects of oral administration of crocetin on damage induced by N-methyl-d-aspartate (NMDA) in the murine retina. Crocetin was orally administered before and after intravitreal injection of NMDA. A histological analysis was conducted by counting the cell number of ganglion cell layer (GCL). Cell apoptosis was assessed by counting cells positive for terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL). Retinal functions were measured in terms of a- and b-wave amplitudes using an electroretinogram (ERG). Activation of caspase-3/7 and cleaved caspase-3 expression were assayed. Calpain activity was evaluated by immunoblotting assays for proteolysis of α-spectrin. NMDA injection decreased the cell number in the GCL, and crocetin at a dose of 100 mg/kg inhibited this reduction. TUNEL-positive cells were observed in both GCL and inner nuclear layer (INL) after NMDA injection, and crocetin inhibited the increase in number of TUNEL-positive cells. ERG analysis showed that both a- and b-wave amplitudes were decreased by NMDA injection. Crocetin inhibited the reduction in the b-wave amplitude, but not in the a-wave. NMDA injection activated caspase-3/7 and increased expression of cleaved caspsase-3 in the GCL and INL, but both of these processes were inhibited by crocetin. NMDA injection also induced cleavage of α-spectrin, but crocetin did not affect this process. These findings indicate that oral administration of crocetin prevented NMDA-induced retinal damage via inhibition of the caspase pathway.