Inhibition of neuroretinal cell death by insulin-like growth factor-1 and its analogs

PURPOSE: Visual loss secondary to retinal ischemia/hypoxia can be a serious complication of diabetic retinopathy, as well as other vascular insults. W e used R28 retinal precursor cells, as well as primary rat retinal cell cul tures, to test whether the neuroprotective growth factor IGF-1 would protec t retinal cells from dying under conditions of hypoxia or serum-starvation. We also utilized three IGF-1 analogs ([LongR3], [Ala31], and [Leu24][Ala31 ]) with altered affinities for the IGF-1 receptor and/or IGF-1 binding prot eins in order to address the mechanism(s) of IGF-1 neuroprotection. METHODS: Retinal cultures were subjected to hypoxia (95% N-2/5% CO2 for 0-8 h), or serum-starvation (0% serum for 48 h). Experimental cultures were pr e-treated for 24 h with 0-100 ng/ml of IGF-1 or its analogs. Retinal cultur es were analyzed for the extent of cell death by trypan blue exclusion assa y, TUNEL in situ, as well as ssDNA analysis specific for apoptosis. RESULTS: IGF-1 and all three IGF-1 analogs tested were able to inhibit neur oretinal cell death at a concentration of 50 ng/ml. Neuroprotection was evi dent under conditions of hypoxia or serum-starvation. CONCLUSIONS: IGF-1, as well as IGF-1 analogs, improves survival of neuroret inal cells in vitro, under conditions of hypoxia or serum-starvation. Since all three IGF-1 analogs inhibit cell death to some degree, we interpret th ese results to mean that IGF-1-mediated inhibition of cell death does not d epend upon strong affinities for the IGF-1 receptor or IGF-1 binding protei ns. Further studies will reveal additional information as to the pathways r esponsible for IGF-1-mediated neuroprotection of retinal cells.