The effects of flavonoids and phenolic acids on superoxide dismutase activity

Flavonoids and phenolic acids are compounds ubiquitous in photosynthesizing organisms and many in vitro studies have demonstrated significant interferences with mammalian enzyme systems and signaling pathways. In this study, we investigated the effects of 35 flavonoids (flavones, flavonols, flavanones and isoflavonoids) and 9 phenolic acids on the activity of superoxide dismutase (SOD), which is one of the key enzymes in antioxidant defense system. All experiments were performed on differentiated THP-1 cell line (human macrophage-like cells). Cytotoxicity of chosen compounds was determined using bioluminiscent cytotoxicity assay by which the release of adenylate kinase from damaged cells was measured, while [6-H³] thymidine incorporation assay was used to determine the effect of tested compounds on cell proliferation. The effects of chosen polyphenols in 30µM concentration on SOD activity were measured 24 hours after the addition of compounds using RANSOD® antioxidant kit. Lipopolysacharide from E. coli was used as a positive and un-stimulated cells as a negative control. None of the tested polyphenols exhibited cytotoxic effects after 24 hours of incubation. Generally, flavones and flavonols suppressed the proliferation of differentiated THP-1 cells, flavanones and isoflavonoids exhibited mild inhibitory effects, while phenolic acids did not affect the proliferation. Among all tested compounds only morin suppressed SOD activity, since 25% inhibition comparing to the un-stimulated cells was found when the cells were exposed to this flavonol. The majority of the tested substances induced SOD activity (1.2 to 2 times comparing to the negative control) while acacetin, baicalein and diosmetin were shown to be powerful inducers of SOD since they enhanced the enzyme activity more than twofold.