fig2

Figure 2. The influence of epicatechin on cytotoxic effect of curcumin in HL-60 cells. Cells were incubated with increased concentrations of epicatechin (A) and/or curcumin in concentration of 10 (A) or 20 μmol/L (B) for 20 h. Control cells were incubated with DMSO only. Cytotoxicity was investigated by using propidium iodide staining and analyzed in flow cytometer. Interaction between investigated compounds was analyzed by Calcusyn software separately for Cur10 μmol/L + EC 50 μmol/L - 1 mmol/L (C) and for Cur20 μmol/L + EC 50 μmol/L - 1 mmol/L (D). The lower concentrations of epicatechin (50-500 μmol/L) cooperated synergistically with curcumin (CI < 1) increasing cytotoxic effect (C) and (D). However high concentrations of epicatechin (750 μmol/L and 1 mmol/L) exerted antagonistic effect with curcumin (CI > 1, (C) and (D)), because their effect together with curcumin was less than the sum of the individual components in these concentrations. Values are means ± SEM, *P < 0.05, **P < 0.01, ***P < 0.001; vs. control; ^#P < 0.05, ^##P < 0.01, ^###P < 0.001 vs. Cur; ⁺⁺P < 0.01 vs. EC500; P = 0.07 vs. Cur. (Mann-Whitney test). Cur: curcumin; EC: epicatechin; CI: combination index, × combination of investigated compounds