Fig. 1.

Therapeutic approaches to increase cellular NAD⁺ levels. The three major pathways for the biosynthesis of NAD⁺ are shown. Approaches to increase NAD⁺ levels include administering the metabolites, NA, NR, or NMN to increase their levels or increasing NAMPT activity (up arrowheads). In addition, down-regulation (down arrowhead) of the NAD⁺ consumers, PARP and CD38/157, will result in increased cellular NAD⁺ levels. The increased NAD⁺ levels will increase the levels and activity of NAD⁺-dependent SIRT1 and other sirtuins with beneficial metabolic outcomes.