[The influence of quercetin on the activity of purified 20S, 26S proteasome and proteasomal activity in isolated cardiomyocytes].

For the clarification of the effect of quercetin on the proteasome experiments were performed using purified 20S proteasome, 26S proteasome from the proteasomal fraction II (PF II), as well as cardiomyocyte culture which underwent anoxia-reoxygenation. In the experiments with purified 20S proteasome it was shown, that quercetin in a dose-dependent manner inhibits all three peptidase activities of the proteasome, comparable to a specific proteasome inhibitor. The highest quercetin inhibition was observed in the case of chymotrypsin-like activity of proteasome. In the same way quercetin inhibited the activity of 26S proteasome from the PF II. Quercetin decreased trypsin-like (by 26%, p = 0.03), chymotrypsin-like (by 63.7%, p = 0.04) and peptidyl-glutamyl peptide-hydrolyzing (by 34.2%, p = 0.16) activities in the cardiomyocytes culture. It appears, that quercetin and its water-soluble analogue korvitin affect the cardiomyocytes in the same manner, as specific proteasome inhibitors clasto-lactacystin-beta-lactone. In the concentrations 5 and 10 mM quercetin and korvitin resulted in the decrease of the amount of living cardiomyocytes, increasing the amount of necrotic and apoptotic cells. In the concentration 2.5 mM quercetin and korvitin significantly abolished damaging effect of anoxia-reoxygenation, decreasing the amount of necrotic and apoptotic cells. These data suggest that the mechanisms of cardioprotective effect of quercetin connected with inhibition of proteasome.