Preconditioning with carbon monoxide inhalation promotes retinal ganglion cell survival against optic nerve crush via inhibition of the apoptotic pathway.

Optic neurodegeneration, in addition to central nervous trauma, initiates impairments to neurons resulting in retinal ganglion cell (RGC) damage. Carbon monoxide (CO) has been observed to elicit neuroprotection in various experimental models. The present study investigated the potential retinal neuroprotection of preconditioning with CO inhalation in a rat model of optic nerve crush (ONC). Adult male Sprague-Dawley rats were preconditioned with inhaled CO (250 ppm) or air for 1 h prior to ONC. Animals were euthanized at 1 or 2 weeks following surgery. RGC densities were quantified by hematoxylin and eosin (H&E) staining and FluoroGold labeling. Visual function was measured via flash visual evoked potentials (FVEP). Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) staining, and caspase-9 and caspase-3 activity in the retinas, were assessed at 2 weeks post-ONC. The RGC density of CO + crush rats was significantly increased compared with that of the corresponding crush-only rats at 2 weeks (survival rate, 66.2 vs. 48.2% as demonstrated by H&E staining, P<0.01; and 67.6 vs. 37.6% as demonstrated by FluoroGold labeling, P<0.05). FVEP measures indicated a significantly better-preserved latency and amplitude of the P1 wave in the CO + crush rats compared with the crush-only rats. The TUNEL assays demonstrated fewer apoptotic cells in the CO + crush group compared with the crush-only group, accompanied by the suppression of caspase-9 and caspase-3 activity. The results of the present study suggested that inhaled CO preconditioning may be neuroprotective against ONC insult via inhibition of neuronal apoptosis.