Excessive exposure of the eye to ultraviolet B light (UVB) leads to
corneal edema and opacification because of the apoptosis of the corneal endothelium. Our previous study found that
nicotinamide (NIC), the precursor of
nicotinamide adenine dinucleotide (
NAD), could inhibit the endothelial-mesenchymal transition and accelerate healing the
wound to the corneal endothelium in the rabbit. Here we hypothesize that NIC may possess the capacity to protect the cornea from UVB-induced endothelial apoptosis. Therefore, a mouse model and a cultured cell model were used to examine the effect of NAD+ precursors, including NIC,
nicotinamide mononucleotide (NMN), and
NAD, on the UVB-induced apoptosis of corneal endothelial cells (CECs). The results showed that UVB irradiation caused apparent
corneal edema and cell apoptosis in mice, accompanied by reduced levels of NAD+ and its key biosynthesis
enzyme,
nicotinamide phosphoribosyltransferase (NAMPT), in the corneal endothelium. However, the subconjunctival injection of NIC, NMN, or NAD+ effectively prevented UVB-induced tissue damage and endothelial cell apoptosis in the mouse cornea. Moreover, pretreatment using NIC, NMN, and NAD+ increased the survival rate and inhibited the apoptosis of cultured human CECs irradiated by UVB. Mechanistically, pretreatment using
nicotinamide (NIC) recovered the AKT activation level and decreased the BAX/BCL-2 ratio. In addition, the capacity of NIC to protect CECs was fully reversed in the presence of the AKT inhibitor
LY294002. Therefore, we conclude that NAD+ precursors can effectively prevent the apoptosis of the corneal endothelium through reactivating AKT signaling; this represents a potential therapeutic approach for preventing UVB-induced
corneal damage.