(a) NAD+ concentrations in cardiomyocytes treated with mock (n = 7), DOX (n = 7), or DOX + FK866 (n = 11). **P < 0.01. (b) Sirt1 deacetylase activity in cardiomyocytes treated with mock (n = 4), DOX (n = 5), or DOX + FK866 (n = 5). *P < 0.05, **P < 0.01. (c) Immunoblot analysis of acetylated lysine (Ac-K) and histone H3 in the nuclear fraction of cardiomyocytes treated with mock, DOX, or DOX + FK866. The quantitations of Ac-K/histone H3 are shown as bar graphs (n = 8, in each group). **P < 0.01. (d) Cell viability in cardiomyocytes treated with mock, DOX, or DOX + FK866 (n = 6, in each group). **P < 0.01. (e) The mRNA levels of mitochondria-associated genes in cardiomyocytes treated with mock (n = 7), DOX (n = 7), or DOX + FK866 (n = 5). *P < 0.05 versus mock, **P < 0.01 versus mock, #P < 0.05 versus DOX, ##P < 0.01 versus DOX. (f) NAD+ concentrations in cardiomyocytes treated with mock (n = 4), DOX (n = 3), or DOX + NMN (n = 4). *P < 0.05, **P < 0.01. (g) Sirt1 deacetylase activity in cardiomyocytes treated with mock (n = 4), DOX (n = 5), or DOX + NMN (n = 5). *P < 0.05, **P < 0.01. (h) Immunoblot analysis of Ac-K and histone H3 in cardiomyocytes treated with mock, DOX, or DOX + NMN. The quantitations of Ac-K/histone H3 are shown as bar graphs (n = 8, in each group). *P < 0.05, **P < 0.01. (i) Cell viability in cardiomyocytes treated with mock, DOX, or DOX + NMN (n = 6, in each group). **P < 0.01. (j) The mRNA levels of mitochondria-associated genes in cardiomyocytes treated with mock (n = 7), DOX (n = 5), or DOX + NMN (n = 5). **P < 0.01 versus mock, #P < 0.05 versus DOX, ##P < 0.01 versus DOX.