NAMPT and osteoarthritis: NR has been shown to play a pivotal role in the interplay between hypoxia-inducible factor-2α (HIF-2α) and the nicotinamide phosphoribosyltransferase (NAMPT)-nicotinamide adenine dinucleotide-sirtuin axis (SIRT), contributing to osteoarthritis (OA) cartilage deterioration.