Vanillin attenuates glycation associated modifications and partially restores iron binding and release properties in human serum transferrin: insights from biophysical and computational studies

Protein glycation, especially under hyperglycemic conditions observed during diabetes, results in the formation of advanced glycation endproducts (AGEs) as a result of reaction between reducing sugars or dicarbonyls and free amino groups of proteins. The presence of AGEs and the accompanied oxidative stress contribute to the progression and severity of diabetic complications. Transferrin, the major serum glycoprotein involved in transport of iron between cellular sites of absorption and utilization undergoes variable glycation in diabetic patients and in vitro conditions. Glycated transferrin has been attributed with impaired iron binding property under in vitro and in vivo conditions. Here, we report the glycation inhibition observed in methylglyoxal glycated transferrin by vanillin. From our experiments, vanillin showed hindered AGE formation notably in vesperlysine and total AGEs and curtailed advanced oxidation protein product formation. Further glycation induced fibrillation and extent of arginine modification was also reduced in the presence of vanillin. Glycated transferrin did not exhibit enhanced iron binding which was partially restored in the presence of vanillin. Also, glycated transferrin showed marked increase in iron release even at mild acidic conditions while vanillin treatment retained native-like iron release property. The binding of vanillin to transferrin as assessed by fluorescence quenching studies revealed a binding affinity of 0.187 ± 0.04 × 105 M−1 with one binding site. And in silico molecular dynamics studies showed continuous interaction between vanillin and transferrin and molecular mechanics Poisson Boltzmann surface area binding energy calculations showed the electrostatic energy as the highest contributor. Thereby, vanillin exerts reduced glycation associated effects against glycated transferrin and prevents subsequent oxidative damage and aggregates formation.