Interaction of pirenzepine with bovine serum albumin and effect of β-cyclodextrin on binding: A biophysical and molecular docking approach.

Studying the interaction of therapeutic molecules with serum albumin is important to understand their biopharmaceutics, pharmacokinetics and toxicity as well as their relation with the structure and function of protein. The biomolecular interaction of an anti-spasmodic drug, pirenzepine with bovine serum albumin (BSA) was investigated using multi-spectroscopic, calorimetric and docking studies. Fluorescence quenching of BSA on interaction with pirenzepine revealed the static mode of quenching. Pirenzepine exhibited a moderate binding to serum albumin with the binding constant value in the order of 10 M. Based on the Forster's non-radiative energy transfer theory, the average binding distance between BSA and pirenzepine was calculated. Competitive site marker experiments demonstrated that pirenzepine binds to the sudlow site III located in subdomain IB of BSA. Circular dichroic spectroscopy indicated secondary structural changes in BSA while three-dimensional fluorescence spectroscopy showed the microenvironmental perturbations in the structure of BSA on interaction with pirenzepine. Moreover, thermodynamic parameters obtained from isothermal titration calorimetry suggested that the interaction between pirenzepine and BSA was spontaneous and hydrophobic interactions played the major role in stabilizing the complex. Additionally, the effect of inclusion compound, β-cyclodextrin on pirenzepine-BSA interaction was studied. As pirenzepine is involved in drug-drug interactions, β-cyclodextrin forms an inclusion complex with pirenzepine and prevents drug-drug interactions, thereby, enhancing the therapeutic effect of pirenzepine. Some common metal ions have also been found to interfere with pirenzepine-BSA interaction. The above experimental results further corroborated the molecular modelling studies.