Modest exercise boosts tryptophan metabolism and NAD+ levels in the aged liver. (A) Graph depicting mean NAD+ levels measured in the livers of sedentary and exercised nfkb1−/− mice. (B) Simplified diagram of the de novo tryptophan metabolism pathway (C) Graph depicting mean tryptophan levels measured in the livers of sedentary and exercised nfkb1−/− mice (sedentary, n = 13; exercised, n = 16). (D) Graphs depicting relative mRNA expression of TDO2, IDO1, and IDO2 in the liver. (E) Graph depicting mean KYN levels measured in the livers of sedentary and exercised nfkb1−/− mice. (F) Graph depicting relative mRNA expression of KMO in livers of sedentary and exercised nfkb1−/− mice. (G) Graph depicting relative mRNA expression of genes involved in the tryptophan metabolism pathway: KYNU, KAT1, HAAO, and QPRT in livers of sedentary and exercised nfkb1−/− mice. Data of one study (sedentary, n = 13; exercised, n = 16). Data are means ± SEM. Statistical significance was determined using an unpaired two-tailed Student t test. *p < 0.05, **p < 0.01, ***p < 0.001 compared with control.