Influence of quercetin and luteolin on the activity of the catalase: study ex vivo about erythrocytes in smokers and non-smokers

Abstract

Flavonoids are a group of polyphenolic compounds with different chemical structure and properties. These compounds may scavenge free radical species and other oxidants. In previous studies, we have observed that some polyphenols are able to cross the erythrocyte’smembrane and this process is influenced by the plasmatic albumin; in fact quercetin intracellular concentrations is albumin dose depending. The influence of flavonoids on catalase activity has been reported in some papers but the results are contradictory. Some authors have found an increase of catalase activity in cell in the presence of flavonoids. Others have observed any effect or even a decrease of catalase activity.The present work is based on a study of Krych’s, in which the influence of flavonoids on catalase in model system has been evaluated. Aim of this work was to study the role of red body cells in the antioxidant balance. The primary goal was to evaluate the antioxidant status of no-smokers and ever-smokers healthy subjects by the determination of the plasma antioxidant capacity and of the catalase activity of erythrocyte and then to evaluate if flavonoids (quercetin and luteolin) are able to modify the enzyme activity. This is a pilot study. Nine healthy subjects, aged 24-55 years were recruited. None of the subjects had any pathologies at the time of sampling. We assayed the CAT activity in erythrocytes isolated from whole blood of the subjects by the colorimetric assay and the plasma antioxidant capacity using the spectrophotometric method known crocin bleaching assay. The catalase activity was performed in human erythrocytes (control) and after the incubation of them with the flavonoids (quercetin and luteolin). The flavonoids were efficiently taken up by human erythrocytes in dose-depending manner. There was no significant difference in the percent accumulation of both molecules (quercetin and luteolin) inside the erythrocytes when incubated at the same concentration of 50μM. In physiologic condition the catalase activity varies from 28.6 mU/g protein to 40.6 mU/g protein. Data have shown that CAT activity of erythrocytes was significantly lower in ever smokers than in nosmokers. It was also found that Quercetin at the concentration of 100μM is able to increase the catalase levels in ever-smokers up to the normal values observed in no smokers. The study on the luteolin has not produced the same effects. In fact, Luteolin is able to reduce the CAT levels in no-smokers subject according with the data from Krych. The different actions of compounds on catalase can been explained as consequence of flavonoid interaction with enzymatic protein. The inhibiting action of the luteolin can be a consequence of a conformational change which occurs upon the flavonoid binding to catalase. This interaction changes the geometry of the substrate channel and thus inhibits the reaction of H2O2 with the heme center. Plasma antioxidant capacity was lower in no smokers than in smokers. An inverse correlation has been found between age and plasma antioxidant capacity. From the results of this study affirms that an oxidative stress condition is present in ever-smokers respect to non-smokers, but the quercetin is able to restore the erythrocyte oxidative stress condition of ever-smokers back to the normality. Further studies are necessary in the future to better investigate the role of luteolin on the catalase activity of human erythrocytes.