Antioxidant Activity of Ruthenium Cyclopentadienyl Complexes Bearing Succinimidato and Phthalimidato Ligands

Abstract

In these studies, we investigated the antioxidant activity of three ruthenium cyclopentadienyl complexes bearing different imidato ligands: (η⁵-cyclopentadienyl)Ru(CO)₂-N-methoxysuccinimidato (1), (η⁵-cyclopentadienyl)Ru(CO)₂-N-ethoxysuccinimidato (2), and (η⁵-cyclopentadienyl)Ru(CO)₂-N-phthalimidato (3). We studied the effects of ruthenium complexes 1-3 at a low concentration of 50 µM on the viability and the cell cycle of peripheral blood mononuclear cells (PBMCs) and HL-60 leukemic cells exposed to oxidative stress induced by hydrogen peroxide (H₂O₂). Moreover, we examined the influence of these complexes on DNA oxidative damage, the level of reactive oxygen species (ROS), and superoxide dismutase (SOD) activity. We have observed that ruthenium complexes 1-3 increase the viability of both normal and cancer cells decreased by H₂O₂ and also alter the HL-60 cell cycle arrested by H₂O₂ in the sub-G1 phase. In addition, we have shown that ruthenium complexes reduce the levels of ROS and oxidative DNA damage in both cell types. They also restore SOD activity reduced by H₂O₂. Our results indicate that ruthenium complexes 1-3 bearing succinimidato and phthalimidato ligands have antioxidant activity without cytotoxic effect at low concentrations. For this reason, the ruthenium complexes studied by us should be considered interesting molecules with clinical potential that require further detailed research.

Keywords: DNA oxidative damage; ROS; SOD activity; cell cycle; hydrogen peroxide; phthalimide; ruthenium metallocarbonyl complexes; succinimide.

Figure 1

The structures of the ruthenium complexes 1–3.

Figure 2

Effect of ruthenium complexes 1–3 at 50 µM on the viability of PBMCs and HL-60 cells incubated with H₂O₂. The viability for individual samples was calculated relative to negative control (untreated cells) ± SD. Cell viability in the control was taken as 100%, n = 6, * p < 0.05, *** p < 0.001 vs. negative control, ^## p < 0.01, ^### p < 0.001 vs. H₂O₂.

Figure 3

Effect of ruthenium complexes 1–3 at 50 μM on H₂O₂-induced DNA damage in PBMCs and HL-60. The figures show mean results ± SEM, n = 100; *** p < 0.001 vs. negative control; # p < 0.05, ### p < 0.001 vs. H₂O₂.

Figure 4

Changes in reactive oxygen species (ROS) level in PBMCs and HL-60 cells pre-incubated with ruthenium complexes 1–3 at 50 μM for 24 h at 37 °C and then incubated with 1 mM or 5 mM H₂O₂ at 37 °C. Each value represents the mean ± SD, n = 6; * p < 0.05, ** p < 0.01, *** p < 0.001 vs. negative control; ## p < 0.01, ### p < 0.001 vs. H₂O₂.

Figure 5

Superoxide dismutase activity in PBMCs and HL-60 cells pre-incubated for 24 h at 37 °C with ruthenium complexes 1–3 at 50 µM and then incubated with H₂O₂ at 0.25 mM in the case of PBMCs and 0.1 mM in the case of HL-60 cells. The figure shows the mean results ± SD, n = 3; * p < 0.05, and *** p < 0.001 vs. negative control; ^### p < 0.001 vs. H₂O₂. Data were normalized to the negative control, which was assigned as 100% of the SOD activity.