Acetaminophen interacts with human hemoglobin: optical, physical and molecular modeling studies

Abstract

Acetaminophen, a widely used analgesic and antipyretic drug has ample affinity to bind globular proteins. Here, we have illustrated a substantive study pertaining to the interaction of acetaminophen with human hemoglobin (HHb). Different spectroscopic (absorption, fluorescence, and circular dichroism (CD) spectroscopy), calorimetric, and molecular docking techniques have been employed in this study. Acetaminophen-induced graded alterations in absorbance and fluorescence of HHb confirm their interaction. Analysis of fluorescence quenching at different temperature and data obtained from isothermal titration calorimetry indicate that the interaction is static and the HHb has one binding site for the drug. The negative values of Gibbs energy change (ΔG⁰) and enthalpy changes (ΔH⁰) and positive value of entropy change (ΔS⁰) strongly suggest that it is entropy-driven spontaneous and exothermic reaction. The reaction involves hydrophobic pocket of the protein which is further stabilized by hydrogen bonding as evidenced from ANS and sucrose binding studies. These findings were also supported by molecular docking simulation study using AutoDock 4.2. The interaction influences structural integrity as well as functional properties of HHb as evidenced by CD spectroscopy, increased rate of co-oxidation and decreased esterase activity of HHb. So, from these findings, we may conclude that acetaminophen interacts with HHb through hydrophobic and hydrogen bonding, and the interaction perturbs the structural and functional properties of HHb.

Keywords:

• acetaminophen
• human hemoglobin
• spectroscopy
• isothermal titration calorimetry
• molecular modeling

Acknowledgment

The authors are indebted to Prof. P. K. Das of The Indian Association for the Cultivation of Science, Kolkata for providing the access to CD Spectrometer; to the Central Instrumental Facility of The Bose Institute, Kolkata for fluorescence spectrophotometry; and also to Mr. Souvik Roy, technical officer, DBT-CU-IPLS, central facility of University of Calcutta for cooperating in accessing the ITC. The authors are also grateful to Prof. Ansuman Lahiri, Professor of the department of Biophysics, Molecular Biology and Bioinformatics, University of Calcutta, and his research fellow, Mr. Aditya Kumar Sarkar for helping in AutoDock analysis.