Journal
EUROPEAN JOURNAL OF PHARMACEUTICAL SCIENCES
Volume 112, Issue -, Pages 122-131Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.ejps.2017.11.013
Keywords
Ibuprofen; Human serum albumin; Thermal unfolding; Differential scanning calorimetry; Fourier transform infrared spectroscopy; Molecular dynamics simulation
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Ibuprofen is one of the most used anti-inflammatory drugs, and it is transported in the blood by human serum albumin, a major plasmatic protein with a peculiar adaptability in the binding of several different ligands. We have characterized the interaction between albumin and ibuprofen, either in racemic mixture, or in the S(+) and R(-) enantiomeric forms, by using differential scanning calorimetry, attenuated total reflectance Fourier transform infrared spectroscopy, and molecular dynamics simulation. The results show that increasing concentrations of ibuprofen (up to sixfold drug/protein molar ratio) improve the protein resistance to thermal unfolding without altering the secondary structure. Deconvolution of the calorimetric thermal profiles at different albumin/ibuprofen molar ratios demonstrates a selective stability of the protein domains where the binding sites of the drug are localized. At the highest ibuprofen concentration, the melting temperature increased by about 10 degrees C with respect to the drug-free protein, whereas the unfolding enthalpy maintains an almost constant value. Furthermore, the degree of protein stabilization depends upon the chirality of the drug, and the R (-) enantiomer is more effective compared to the S(+) form. The stability is supported by molecular dynamics simulations, showing that ibuprofen maintains a stable coordination in the most favorable binding sites, leading to a more compact protein structure at high temperature. The overall results attest that the binding of ibuprofen determines on albumin a stereoselective and domain-specific stabilization with a predominantly entropic character, contributing to clarify significant aspects of the molecular mechanism of protein/drug interaction.
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