Glycoxidative damage to human DNA: Neo-antigenic epitopes on DNA molecule could be a possible reason for autoimmune response in type 1 diabetes.

Advanced glycation end-products (AGEs) are known to be mutagenic, diabetogenic and vascular disease risk factors. Methylglyoxal (MG) is a dicarbonyl species that reacts with biological macromolecule (proteins, DNA and lipids) to give AGEs. Nonenzymatic glycation of MG with lysine (Lys) in the presence of copper (Cu2+) is reported to generate reactive oxygen species (ROS) capable of causing DNA damage. We show that DNA modification in MG–Lys–Cu2+ system results in the generation of strand breaks, base modification, hyperchromicity and increased fluorescence intensity. Superoxide generation in the MG–Lys system was found to be significantly higher when compared with that in the MG and Lys alone. Moreover, d-penicillamine and pyridoxal phosphate significantly inhibited the formation of glycation products. The presence of a major DNA glycation adduct, N2-carboxyethyl-2′-deoxyguanosine (CEdG), was detected by high performance liquid chromatography (HPLC) and confirmed by nuclear magnetic resonance (NMR). As reported earlier, modified DNA (MG–Lys-Cu2+-DNA) was highly immunogenic in experimental animals. Furthermore, induced anti-MG–Lys–Cu2+–DNA antibodies were effective probe for detecting glycoxidative lesions in human genomic DNA of type I diabetes patients. Our results clearly imply that interaction of MG–Lys and Cu2+ leads to the formation of AGEs and also the production of potent ROS, capable of causing DNA damage, thereby playing an important role in diabetes mellitus. [ABSTRACT FROM AUTHOR]