Studies on the effect of quercetin and nitrates on the redox homeostasis using in vitro model

• The influence of quercetin and sodium nitrate on the redox homeostasis was studied.
• The simultaneous presence of quercetin and sodium nitrate disturbs the oxidation–reduction homeostasis in fibroblasts.
• An increase in the activity of SOD, GPx, GR and NOS enzymes and NO concentration was determined.
• The change in biological parameters depends on quercetin concentration.

Antioxidants are widely considered to be a preventive measure for many diseases and beneficial for health. However, an increasing number of reports suggest a lack of any influence by antioxidants on health or even harmful pro-oxidative effects of antioxidants. In most cases, the research was conducted with respect to a chosen antioxidant, without considering the presence of other chemical substances present in food, with which these compounds may react. The aim of this work was to determine whether and to what extent the simultaneous presence of quercetin and sodium nitrate influences oxidative–reductive homeostasis in fibroblast cultures. Superoxide dismutase (SOD), glutathione peroxidase (GPx), glutathione reductase (GR), and nitric oxide synthase (NOS) activities were measured together with nitric oxide (NO) concentration and total antioxidant status (TAS). An increase in the activity of all the enzymes measured and in the NO concentration was determined compared with the control culture. The most prominent changes were observed at the highest quercetin concentration. These results indicate that the simultaneous presence of quercetin and sodium nitrate disrupts the oxidative–reductive homeostasis in fibroblasts.