Molecular modeling and multispectroscopic studies of the interaction of mesalamine with bovine serum albumin Nahid Shahabadi ⇑ , Soraya Moradi Fili Department of Chemistry, Faculty of Science, Razi University, Kermanshah, Iran highlights  Conformation changes of BSA induced by its interaction with 5-ASA drug.  The drug binds to BSA with a high affinity and transport in the body.  Molecular docking studies confirmed that the drug was located at Sudlowhs site II. graphical abstract In this study, an attempt has been made to study the interaction of mesalamine and its anionic form with bovine serum albumin (BSA) employing UV–vis, fluorometric, circular dichroism (CD) and molecular docking techniques. article info Article history: Received 18 June 2013 Received in revised form 20 August 2013 Accepted 26 August 2013 Available online 12 September 2013 Keywords: Mesalamine BSA Molecular docking abstract The interaction of mesalamine (5-aminosalicylic acid (5-ASA)) with bovine serum albumin (BSA) was investigated by fluorescence quenching, absorption spectroscopy, circular dichroism (CD) techniques, and molecular docking. Thermodynamic parameters (DH < 0 and DS 0) indicated that the hydrogen bond and electrostatic forces played the major role in the binding of 5-ASA to BSA. The results of CD and UV–vis spectroscopy showed that the binding of this drug to BSA induces some conformational changes in BSA. Displacement experiments predicted that the binding of 5-ASA to BSA is located within domain III, Sud- lows site 2, that these observations were substantiated by molecular docking studies. In addition, the docking result shows that the 5-ASA in its anionic form mainly interacts with Gln-416 residue through one hydrogen bond between H atom of 5-ASA anion and the adjacent O atom of the hydroxyl group of Gln-416. Ó 2013 Elsevier B.V. All rights reserved. Introduction Mesalazine (INN, BAN), also known as mesalamine (USAN) or 5- aminosalicylic acid (5-ASA) (Fig. 1), is an anti-inflammatory drug used to treat inflammatory bowel disease, such as ulcerative colitis [1,2]. Sulfasalazine and mesalamine are equally effective in the treatment and maintenance of inflammatory bowel disease. How- ever, the use of sulfasalazine, the oldest and least expensive prep- aration, has become less popular because of side effects including nausea, skin rashes, and reversible oligospermia. The mechanism of action of mesalamine and its metabolites, 5-aminosalicylic acid (5-ASA) and N-acetyl-5-ASA in ulcerative colitis have not been fully elucidated. The 5-ASA moiety is thought to have the major therapeutic action. 5-ASA is thought to work by blocking the pro- duction of prostaglandins and leukotrienes, inhibiting bacterial 1386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.saa.2013.08.110 ⇑ Corresponding author. Tel./fax: +98 831 8360795. E-mail address: nahidshahabadi@yahoo.com (N. Shahabadi). Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 118 (2014) 422–429 Contents lists available at ScienceDirect Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa