Abstract
Fisetin (3,3′,4′,7-tetrahydroxyflavone) is a widely distributed natural flavonol. It interacts with albumin, and thereby generates a fluorescence signal quantitatively. Based on such optical characteristics, we postulated that fisetin was applicable to the quantitation of albumin as an indicator. To establish the fisetin-based albumin assay, we examined the optical properties of fisetin and fisetin–albumin complex. The assay conditions were fine-tuned to fit for the actual concentration of serum albumin and to generate an optimal signal with a high signal-to-background ratio. The reaction between fisetin and albumin was linear in a wide range of concentrations. Non-protein serum components did not interfere with the reaction. The reactivity of fisetin was apparently specific for albumin among serum proteins. Both plasma and serum were compatible with the assay. The samples could be stored in a refrigerator or a freezer without the loss of reactivity toward fisetin. The generation and decay rates of the signal were acceptable for manual handling. The recovery of fortified albumin in serum was confirmed and the assay was validated with human sera. Fisetin-based albumin assay is suitable for clinical laboratory testing, considering the simple and short procedure, high specificity and sensitivity, linearity over a wide range of albumin concentrations, and, presumably, potential automatability.
Highlights
Albumins are simple, water-soluble proteins present in body fluids and tissues
To establish the fisetin-based albumin assay, we examined the optical properties of fisetin and fisetin–Human serum albumin (HSA) complex, optimized the reaction condition, and tested the specificity of fisetin for albumin and the stability of the fluorescence signal
A fisetin solution of 30 μM was prepared with phosphate-buffered saline (PBS; 154 mM NaCl, 5.6 mM Na2HPO4, 1 mM KH2PO4, pH 7.4) or borate buffer solution (BBS; 0.1 M Na2B4O7, adjusted to pH 9.0 using 0.1 M H3BO3) with or without 5 mg/mL HSA
Summary
Water-soluble proteins present in body fluids and tissues. They are most commonly found in blood plasma, in which they are often referred to as serum albumin. The reference methods for serum albumin measurement are immunochemical tests linked to nephelometry or turbidimetry [8] They are relatively specific, but are time-consuming and less cost-effective. Fisetin (3,3 ,4 ,7-tetrahydroxyflavone) is a widely distributed natural flavonol found in plants, including fruits and vegetables It was studied for biological functions, such as neurotrophic, anti-inflammatory, and other health-beneficial effects [15]. To establish the fisetin-based albumin assay, we examined the optical properties of fisetin and fisetin–HSA complex, optimized the reaction condition, and tested the specificity of fisetin for albumin and the stability of the fluorescence signal. We validated this novel assay with the standard addition method and human sera
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