CD38 and sarcopenia: Since NR and NAD+ also play important roles in the regulation of NAD+-consuming enzymes, including sirtuins, PARPs, and CD38/157 ectoenzymes, and NAD+ biosynthesis mediated by NAMPT and SIRT1 function together to regulate metabolism, NAD+ levels decline during cachexia, causing defects in mitochondrial functions and resulting in sarcopenia (Imai and Guarente, 2014).