Date Published: March 20, 2013
Publisher: Public Library of Science
Author(s): Xia Zhang, Lin Li, Zhenbo Xu, Zhili Liang, Jianyu Su, Jianrong Huang, Bing Li, Rizwan Hasan Khan. http://doi.org/10.1371/journal.pone.0059106
Bovine serum albumin (BSA) contains high affinity binding sites for several endogenous and exogenous compounds and has been used to replace human serum albumin (HSA), as these two compounds share a similar structure. Naringin palmitate is a modified product of naringin that is produced by an acylation reaction with palmitic acid, which is considered to be an effective substance for enhancing naringin lipophilicity. In this study, the interaction of naringin palmitate with BSA was characterised by spectroscopic and molecular docking techniques.
The goal of this study was to investigate the interactions between naringin palmitate and BSA under physiological conditions, and differences in naringin and naringin palmitate affinities for BSA were further compared and analysed. The formation of naringin palmitate-BSA was revealed by fluorescence quenching, and the Stern-Volmer quenching constant (KSV) was found to decrease with increasing temperature, suggesting that a static quenching mechanism was involved. The changes in enthalpy (ΔH) and entropy (ΔS) for the interaction were detected at −4.11±0.18 kJ·mol−1 and −76.59±0.32 J·mol−1·K−1, respectively, which indicated that the naringin palmitate-BSA interaction occurred mainly through van der Waals forces and hydrogen bond formation. The negative free energy change (ΔG) values of naringin palmitate at different temperatures suggested a spontaneous interaction. Circular dichroism studies revealed that the α-helical content of BSA decreased after interacting with naringin palmitate. Displacement studies suggested that naringin palmitate was partially bound to site I (subdomain IIA) of the BSA, which was also substantiated by the molecular docking studies.
In conclusion, naringin palmitate was transported by BSA and was easily removed afterwards. As a consequence, an extension of naringin applications for use in food, cosmetic and medicinal preparations may be clinically and practically significant, especially in the design of new naringin palmitate-inspired drugs.
Naringin (4′, 5, 7-trihydroxy flavonone 7-rhamnoglucoside) is a flavonone glycoside (Fig. 1A) that is mainly found in grapefruit and other citrus fruits. It gives the grapefruit or citrus fruit typical bitter taste. As a member of flavonoid family, naringin exhibits effects such as antioxidant , anti-inflammatory , anti-microbial , hepatoprotective , and anticancer activities . Naringin affinity for proteins, enzymes, DNA, RNA or particular cell types, as well as its ability to penetrate the cell membrane determines its biological effects . In vitro experiments have been carried out to verify naringin binding to human serum albumin (HSA) and bovine serum albumin (BSA), as well as transport by these proteins, which is pivotal in the design of new naringin-inspired drugs –. However, the practical application of naringin has been limited by its poor solubility and stability in lipidic environments. Previous investigators tried to modify its degree of lipophilicity by inducing suitable chemical radicals into naringin structure –. Aliphatic groups were usually used to esterify flavonoid hydroxyl radicals in order to increase their solubility in oils, fats and lipophilic media, as well as their effectiveness. A naringin acylation reaction with a fatty acid is expected to effectively and manageably enhance its lipophilicity, thereby expanding its use in food, cosmetic and medicinal preparations. Palmitic acid is one of the most common saturated fatty acids in animals and plants and is widely used in esterification processes. Naringin palmitate has been synthesized by lipase-catalyzed acylation –, and an ester bond from palmitic acid has been identified to present on the C-6′′ of the glucose moiety of the naringin glucose moiety (Fig. 1B). The degree of lipophilicity in naringin palmitate is higher than in naringin, a property that has exhibited an advantage in the transports and metabolic processes during drug therapy. However, the affinity and interaction mechanisms of naringin palmitate to proteins still remain poorly understood, which hinders its application in clinical treatment. Hence, further investigations of naringin palmitate are significant and will undoubtedly aid in understanding the transports and metabolic processes of modified-flavonones in herbal medicine.