Effects of novel quercetin derivatives on sarco/endoplasmic reticulum Ca2+-ATPase activity.

OBJECTIVES: We examined effect of novel quercetin derivatives on sarcoplasmic reticulum (SR) Ca-ATPase activity isolated from skeletal muscles and their potential to prevent injury of SERCA induced by peroxynitrite that is elevated in multiple pathological processes.

METHODS: SR was isolated by ultracentrifugation, ATPase activity of SERCA was measured by NADH-coupled enzyme assay. Sulfhydryl and carbonyl groups content was determined to test oxidation of SERCA. Conformational changes in ATP and calcium binding site were assessed using specific fluorescent labels.

RESULTS: Di(diacetylcafeoyl)-mono-(monoacetylcafeoyl) quercetin (DACQ) restored and diquercetin significantly decreased activity of SERCA in the presence of peroxynitrite. Diquercetin significantly decreased SERCA activity in absence of peroxynitrite. All tested quercetin derivatives decreased thiol group content of SR and caused change in SERCA conformation. Significant decrease of protein carbonyls was observed in SERCA treated with di(diacetylcafeoyl)-mono-(monoacetylcafeoyl) quercetin in the presence of peroxynitrite.

CONCLUSION: DACQ protected SERCA in SR against formation of carbonyls in vitro and protected activity of the pump against inhibition caused by peroxynitrite. However, none tested quercetin derivative did protect SERCA against conformational changes and sulfhydryl group oxidation. Diquercetin inhibited SERCA at relatively low concentrations in the presence of peroxynitrite. Diquercetin and DACQ may prove to be beneficial in treatment of cancer and inflammatory diseases, respectively.