Understanding the mechanism of non-enzymatic glycation inhibition by cinnamic acid: an in vitro interaction and molecular modelling study

Under hyperglycaemic conditions non-enzymatic glycation of proteins gives rise to advanced glycation end products (AGEs). The AGEs thus formed generate free radicals, which foster the development of diabetes and its associated complications. Inhibition of glycation is expected to play a role in controlling diabetes. Plant derived antioxidants like cinnamic acid (CA) are known for limiting AGE formation, however, the mechanism involved is poorly understood. Therefore, we aimed to investigate the possible mechanism of inhibition of AGEs formation by CA through various experimental approaches. Glycation of HSA was achieved by incubating the reaction mixture with glucose for 30 days at 37 degrees C. The protein samples were tested for levels of free lysine & thiol groups, carbonyl content and reactive oxygen species (ROS). Interaction between CA and HSA was also studied through various biophysical techniques. Thermodynamic studies showed a strong exothermic interaction between CA and HSA. The positive value of T Delta S degrees and negative value of Delta H degrees indicates that the HSA-CA complex is mainly stabilized by a hydrophobic interaction and hydrogen bond. Further, molecular docking reveals that CA binds to HSA subdomain IIA (Sudlow's site I) with a binding energy of -7.0 kcal mol(-1), nearly the same as obtained in isothermal titration calorimetry (ITC) and fluorescence spectroscopy. The results of various spectroscopic techniques along with molecular docking and examination of many biomarkers highlights the role of CA in preventing disease progression.