Studies on structure and immunology of glycated deoxyribonucleic acid: role in aging and type-2 diabetes

Abstract

In principle, all reducing sugars whether aldoses or ketoses can initiate glycation in vivo. The non-enzymatic reaction between the aldehyde group of reducing sugars and amino groups of proteins, lipids and nucleic acids is known as the Maillard reaction or non-enzymatic glucosylation. The reaction starts with the formation of reversible Schiff base which are then transformed into more stable early glycation products (Amadori products), and further dehydration and rearrangement leads to advanced glycation end products (AGEs). Earlier studies have demonstrated that incubation of DNA with reducing sugars can generate chromophores and fluorophores with spectral properties similar to advanced glycated protein products. Under physiological conditions several DNA adducts are formed upon reaction with reducing sugars. The two diastereomers of N2-carboxyethyl-2and#8242;-deoxyguanosine, CEdGA,B are main and stable reaction products that are formed from variety of glycating agents such as glucose, ascorbic acid, glyceraldehyde (DHA) etc. Introduction of a carboxyethyl- or carboxymethyl group at N2-position of 2and#8242;-deoxyguanosine leads to decrease stability of the N-glycosidic bond. As a consequence, glycated DNA easily undergoes depurination which significantly increases mutation rates and strand breaks. Furthermore, the glycation reaction is accelerated during elevated glucose concentration and become more aggravated in poorly controlled diabetes, contributing to secondary complications. Previous studies have also suggested that glycation process is accompanied by the generation of free radicals which play important role in the pathophysiology of aging and diabetes related complications. In this study, calf thymus DNA was modified (glycated) by D-glucose and analyzed by various biophysical/chemical techniques likeand#8210; UV, fluorescence, NBT reduction, CD, thermal denaturation, HPLC and LC-MS. Agarose gel electrophoresis and nuclease S1 digestibility assay was also performed to assess the modification of DNA.