*2.6. SpD Increased Mitochondrial ATP Production and Oxygen Consumption*

SpD treatment increased intracellular ATP production and the oxygen consumption rate (OCR) in AC16 cells (Figure 8A,B). In addition, SpD treatment increased ATP production in H2O2-treated cells (Figure 8C). Co-treatment with doxorubicin (0.1 μM) and SpD for 24 h increased ATP production as compared to doxorubicin treatment alone (Figure 8D). In our study, SpD showed enhanced antioxidant capacity when compared with equimolar echinochrome A (Figure S6).

**Figure 8.** SpD caused increased ATP production and oxygen consumption rate (OCR) in AC16 cells. (**A**) SpD (10 μM) increased ATP production in AC16 cells. D-galactose (10 mM) was added to reduce cytosolic glycolytic ATP production. By changing energy metabolism in cardiomyocytes by replacing glucose with galactose, high concentrations of galactose could prevent ATP production except that of mitochondria by oxidative phosphorylation (OXPHOS); (**B**) SpD (10 μM) increased OCR. Antimycin A (Ant, 1 μM, a Complex III inhibitor) was used as a cell-based negative control and glucose oxidase (GOx, 1 mg/mL) was used as a cell-free positive control. (**C**) SpD increased ATP levels under H2O2 induced oxidative stress. (**D**) SpD increased ATP production in the presence of doxorubicin (0.1 μM). \* *p* < 0.05 compared with untreated controls, # *p* < 0.05 compared with the D-galactose-treated group.
