Non-enzymatic glycation of proteins: a cause for complications in diabetes

Diabetes mellitus is one of the most common non-communicable diseases, and is the fifth leading cause of death in most of the developed countries. It can affect nearly every organ and system in the body and may result in blindness, end stage renal disease, lower extremity amputation and increase risk of stroke, ischaemic heart diseases and peripheral vascular disease. Hyperglycemia in diabetes causes non-enzymatic glycation of free amino groups of proteins (of lysine residues) and leads to their structural and functional changes, resulting in complications of the diabetes. Glycation of proteins starts with formation of Shiff's base, followed by intermolecular rearrangement and conversion into Amadori products. When large amounts of Amadori products are formed, they undergo cross linkage to form a heterogeneous group of protein-bound moieties, termed as advanced glycated end products (AGEs). Rate of these reactions are quite slow and only proteins with large amounts of lysine residues undergo glycation with significant amounts of AGEs. The formation of AGEs is a irreversible process, causing structural and functional changes in protein leading to various complications in diabetes like nephropathy, retinopathy, neuropathy and angiopathy. The present review discusses about role of glycation in various complications of diabetes.