The Interaction Between Quercetin And Plasma Protein And Effect Of Complex Formation On Biological Activity Of Quercetin

Quercetin(Que),as a natural polyphenol flavonoid,has important physiological activities such as anti-oxidant,anti-cancer,and anti-inflammation,and plays an important role in human health.However,due to its unstable structure,the low bioavailability of Que limits its application in the human body.Copper ion(Cu²⁺)is the trace element with the third content in the human body,and participates in multiple physiological activities.Cu²⁺also have potential cytotoxicity and can generate reactive oxygen species in tissues.Reactive oxygen species-induced oxidative stress will lead to the occurrence of degenerative diseases.In addition,the presence of Cu²⁺may lead to the switch from antioxidant ability of flavonoid to a pro-oxidant.Plasma protein can be used as a natural carrier for bioactive components to improve the activity and stability of bioactive components,and promote their bioavailability.Therefore,plasma protein could be selected as the carrier for Que to form protein-ligand complexes and investigate the effects of the formation of the complexes on the stability of Que and the toxicity of Cu²⁺.The research content of this paper is mainly divided into two parts:1.Firstly,the interaction mechanism between Bovine Serum Albumin(BSA)and Que was studied by fluorescence spectrometry and molecular docking technology.The data were analyzed by Stern-Volmer equation and double logarithmic equation.The results showed that in the presence or absence of Cu²⁺,BSA could interact with Que to form BSA-Cu²⁺-Que di-ligand complex and BSA-Que mono-ligand complex,respectively.The interaction mechanism of BSA and Que was static quenching.Both Cu²⁺and Que were mainly bound to site 1 of BSA.The binding affinity of the two small molecules to BSA was BSA-Que>BSA-Cu²⁺,because Que was a poly-hydroxyl flavonoid that could bind to protein more stably.The stability and antioxidant activities of Que were studied by UV-Vis spectrum.The results showed that the autoxidation of Que was more obvious with the increase of time.The stability of Que in the four different systems was BSA-Que>Que>BSA-Cu²⁺-Que>Que-Cu²⁺,indicating that BSA had a protective effect on the stability of Que,while Cu²⁺promoted the oxidation of quercetin.The scavenging capacity of Que on ABTS radicals was in the order of Que>BSA-Que>Que-Cu²⁺>BSA-Cu²⁺-Que,because BSA masked the hydroxyl group of Que and Cu²⁺induced the switch from antioxidant ability of flavonoid to a pro-oxidant.2.Secondly,the interactions between Que/Cu²⁺and four plasma proteins,BSA,Human Serum Albumin(HSA),Immunoglobulin G(Ig G)and Fibrinogen(FG),were investigated.The experimental methods were described above.The results showed that all of four proteins could bind to Que or Cu²⁺to form protein-monoligand complexes.Both BSA and HSA had much higher affinity to bioactive components than the other two proteins.The quenching mechanisms were based on static quenching combined with nonradiative energy transfer.Compared with BSA,HSA exhibited a more effective protection on the stability of Que and had similar effect on the free radical scavenging capacity.Therefore,these data demonstrate the advantages and possibility of designing HSA carriers for the delivery of bioactive compounds in functional-food and biomedical applications.