Investigation Of Interaction Between Baicalein And Protein And Fluorescent Al³⁺ Sensor

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by cognitive dysfunction and memory impairments. cascade theory" proposed that the aggregation of β-amyloid peptide (Aβ) in senile plaques of AD patients plays crucial roles in the pathological mechanism of Alzheimer’s disease. A broad range of polyphenols may play an important role in preventing and treating various diseases including neuroprotective effects. Polyphenols have potential anti-oxidative activities and were able to inhibit Aβ aggregation and reduced Aβ production. Researches indicated that baicalein was good at anti-inflammation, anti-oxidative and anti-cancer activities. Recently, more and more studies of baicalein have been developed on the treatment of AD. In addition, the metabolic imbalance of transition metal may be an important reason for Aβ deposition. In order to understand the influence of aluminum ion for the AD patients, it is necessary to develop new dynamic methods for monitoring the aluminum ion. The study on the interaction of biological molecules with small drug molecules was the popular topics in life science. Recently, fluorescence spectrometry had been used widely because of the advantages such as high sensitivity, simplicity and rapid response.The main contents were as follows:(1)The interaction between baicalein and β-amyloid protein (Aβ1-42) of different incubation time was studied by UV-vis absorption spectrometry and fluorescence spectrometry. The incubation time was13months,9months,0.5months, and they were named AβⅠ, AβⅡ, AβⅢ， respectively. The results show that Aβ1-42may interact with baicalein and form a new compound. The wavelength for the peak of fluorescence emission of Thioflavin T (ThT) was changed from445nm to481nm when ThT was added in Aβ solution which indicating the β-sheet structure of Aβ fibril. The significant decrease in the intensity of fluorescence at481nm was observed when the baicalein was added in mixed solution of Aβ and ThT, suggesting that the depolymerization of Aβ fibrils happened. And the existing Aβ fibrils are disaggregated by baicalein in a time-and dose-dependent manner. AFM images of the morphologies of the Aβ1-42fibrils obviously changed smaller and more dispersive when baicalein added indicating also the depolymerization of Aβ. The results demonstrate a basis for development of a potential herb drug candidate for the treatment of Alzheimer’s disease (AD).(2) The interaction between baicalein and bovine serum albumin (BSA) was studied by means of UV-vis absorption spectrometry and fluorescence spectrometry. The thermodynamic parameters of the reaction were calculated using Van’t Hoff equation. Besides, the number of binding sites and the apparent binding constants at different temperatures were calculated from fluorescence quenching data using Stern-Volmer equation. Results indicate that baicalein is able to quench the intrinsic fluorescence of BSA via static quenching mechanism. The changes of enthalpy and entropy for the reaction of baicalein and BSA are both above zero, which indicates that their interaction is dominated by intermolecular hydrophobic force. Moreover, baicalein is able to induce the conformational change of BSA. Relevant results could help to better understand the action mechanism as well as absorption and distribution features of drugs at molecular level.(3) A dual-signal sensing system based on the inner-filter effect (IFE) was demonstrated, in which the combination of two signaling mechanisms allows metal binding to turn on two fluorescence emission bands, independently. A proof-of-concept fluorescent ratiometric assay for Al3+in pure aqueous solution is presented. The proposed assay is based on the Al3+-induced color and fluorescence changes of Alizarin red S (ARS) and IFE between ARS and meso-tetra(N-methyl-4-pyridyl) porphine tetratosylate salt (TMPyP). In the absence of Al3+, the absorption spectrum of the ARS in0.2mol·L-1HAc-NaAc buffer (pH5.5) has a strong peak at420nm, significantly overlapping with the excitation of TMPyP. ARS is expected to be capable of functioning as a powerful absorber to tune the emission of TMPyP on account of the spectral overlap. Binding of Al3+with ARS forms a fluorometric ARS/A13+complex and shifts the maximum absorbance from420nm to480nm, which overlaps negligibly with the excitation of TMPyP and turns on the proper emission spectrum for TMPyP. Under the optimum conditions, the fluorescence intensity ratio, F585/F651, responds to Al3+over a dynamic range of0.1～1.5μmol·L-1, with a limit of detection of40nmol·L-1, where F585and F651are the fluorescence intensity at585nm and651nm in the absence or presence of Al3+, respectively. Further application in Al3+-spiked water samples suggested a recovery between95and108%. The fluorescence response is highly selective for Al3+over other metal ions with the addition of thiourea as the masking agent.