Albumin, the major serum protein, plays a variety of functions, including binding and transporting endogenous and exogenous ligands. Its molecular structure is sensitive to different environmental modifiers, among which glucose is one of the most significant. In vivo albumin glycation occurs under physiological conditions, but it is increased in diabetes. Since bovine serum albumin (BSA) may serve as a model protein in in vitro experiments, we aimed to investigate the impact of glucose-mediated BSA glycation on the binding capacity towards gliclazide, as well as the ability of this drug to prevent glycation of the BSA molecule. To reflect normo- and hyperglycemia, the conditions of the glycation process were established. Structural changes of albumin after interaction with gliclazide (0-14μM) were determined using fluorescence quenching and circular dichroism spectroscopy. Moreover, thermodynamic parameters as well as energy transfer parameters were determined. Calculated Stern-Volmer quenching constants, as well as binding constants for the BSA-gliclazide complex, were lower for the glycated form of albumin than for the unmodified protein. The largest, over 2-fold, decrease in values of binding parameters was observed for the sample with 30mM of glucose, reflecting the poorly controlled diabetic state, which indicates that the degree of glycation had a critical influence on binding with gliclazide. In contrast to significant changes in the tertiary structure of BSA upon binding with gliclazide, only slight changes in the secondary structure were observed, which was reflected by about a 3% decrease of the α-helix content of glycated BSA (regardless of glucose concentration) in comparison to unmodified BSA. The presence of gliclazide during glycation did not affect its progress. The results of this study indicate that glycation significantly changed the binding ability of BSA towards gliclazide and the scale of these changes depended on glucose concentration. It may have a direct impact on the free drug fraction and its pharmacokinetic behavior, including the risk of hypoglycemic episodes or unexpected interactions with other ligands. The use of BSA in examining binding effects upon glycation seems to be good model for preliminary research and may be used to identify a potential drug response in a diabetic state.
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