NAD⁺ metabolism and retinal degeneration (Review)

The recent years has revealed an intense interest in the study of nicotinamide adenine dinucleotide (NAD⁺), particularly in regards to its intermediates, such as nicotinamide and nicotinic acid known as niacin, and also nicotinamide riboside. Besides its participation as a coenzyme in the redox transformations of nutrients during catabolism, NAD⁺ is also involved in DNA repair and epigenetic modification of gene expression and also plays an essential role in calcium homeostasis. Clinical and experimental data emphasize the age-dependent decline in NAD⁺ levels and its relation with the onset and progression of various age-related diseases. Maintaining optimal levels of NAD⁺ has aroused a therapeutic interest in such pathological conditions; NAD⁺ being currently regarded as an important target to extend health and lifespan. Based on a systematic exploration of the experimental data and literature surrounding the topic, this paper reviews some of the recent research studies related to the roles of the pyridine nucleotide family focusing on biosynthesis, NAD⁺ deficiency-associated diseases, pathobiochemistry related to retinal degeneration and potential therapeutic effects on human vision as well.