Furthermore, a study in CKD rat models, a 5/6 nephrectomy (5/6 Nx) model and an adenine model, respectively, showed that the level of renal NAD+ and NADH as well as the expression of the three key enzymes in NAD+ biosynthesis, QPRT, and NMNAT1/3 was significantly downregulated in the kidney of the two CKD models. This evidence concerns the gene QPRT and chronic kidney disease.