A structural study on the protection of glycation of superoxide dismutase by thymoquinone

Accumulation of advanced glycation end products (AGEs) in tissues and serum plays important roles in diabetes-associated complications. Therefore, the identification of antiglycating compounds is attracting considerable interest. In this study, the structural changes associated with the glycation of superoxide dismutase (SOD) and its protection by thymoquinone (TQ) have been investigated by biophysical techniques. Incubation of SOD with glucose, methylglyoxal (MG) or both at 37 ̊C resulted in progressive hyperchromicity at 280 nm, intrinsic fluorescence quenching at 310 nm, decrease in negative ellipticity at 208 nm, AGE-specific fluorescence enhancement in the wavelength range 400–480 nm and Thioflavin T (ThT) fluorescence enhancement at 480 nm (fibrillar state enhancement). Therefore, glycation by glucose or MG induced both tertiary and secondary structural changes in SOD and formation of AGEs and fibrils. The changes were more and faster with MG than with glucose since MG is a stronger glycating agent than glucose. TQ offered protection against glucose or MG-induced glycation of SOD as observed by a reduction in the structural changes, formation of AGEs and fibrils. Thus, TQ can be used for reducing diabetic complications many of which are due to protein glycation.